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Whitman, Katharine. "The History and Conservation of Glass Supported and Protected Photographs."

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return to Research from the Andrew W. Mellon Advanced Residency Program in Photograph Conservation at George Eastman House 1999-2009



This research project is intended to provide students of photograph conservation the basic information on the history, manufacture, deterioration and conservation of glass supported photographs. The result is a teaching text for the photograph conservation community. This research has been divided into two parts. The first is a synopsis of glass supported photographs that includes an identification tree; and the second is a discussion of the conservation issues involving glass supported photographs, illustrated with case studies. A case study of the treatment of the interpositive of an Abraham Lincoln interpositive is the basis upon which the rest of the case studies are based. This report is intended to aid the education of conservators, raise interest in research in the area, and promote preservation.

Click here for a formatted PDF of this research.


Glass has been an integral part of the art and science of imaging since the very dawn of photography. Joseph Nicéphore Niépce used glass in some of his early experiments such as the Physautotype in 1822, as did his nephew, Niépce de Saint- Victor, and John Frederick William Herschel. Henry Talbot experimented with albumen on glass. There are more than 20 photographic processes on glass, and when the permutations and variations of these are taken into consideration, the number increases to no fewer than 40 processes. In order to treat photographs properly, one must understand their history and production.

Many of the most historically significant photographs of the 19th and early 20th centuries were shot on glass plates. Mathew Brady’s often seen. civil-war-era photographs, Timothy O’Sullivan’s pioneering images of the American West, Alexander Hesler’s portrait work, and countless other iconic images were all taken with glass plates. These early pioneers saw the advantages of glass as a support structure – it is clear, dimensionally stable, easy to clean, and reusable. However with these advantages also come certain drawbacks – most notably that glass is easily broken and succumbs to chemical deterioration.

The deterioration of glass and glass-supported photographs is not just a modern difficulty; it was recognized historically as well. The importance of high quality glass in photography was an issue revisited many times in the early years of the craft. Having Observed weeping and color shifting skylights and photographs, photographers sought out the best glass for their purposes. Even with the best available glass, broken plates were inevitable. However, conservation of glass-supported photographs was infrequent. Many times copy negatives were made onto a new support and the original was discarded. An example of a historical treatment for broken glass-supported photographs was to sandwich the shards between two sheets of glass and bind the three layers together with tape around the perimeter. Modern conservation of glass supported photographs has not progressed much further. This three-layer treatment is still common practice today.

Given the fact that there are so many historically significant images on glass, and that glass has been omnipresent until as recent as 2001 when Kodak ceased production of T-Max plates, it is surprising that there has been so little research into the conservation of glass-supported photographs. The few studies that have been made are dated, inaccessible, too narrowly focused, or too broadly conceived to be of much use to the photograph conservator. The current philosophies and methods of glass repair need to be questioned and reevaluated, and innovative treatment solutions need to be determined. The current research is an initiative to conserve glass supported photographs. Deteriorated or broken plates will not be returned to their original condition, but they can be conserved.

In August of 2005, a broken interpositive of Abraham Lincoln, made by George B. Ayres, after Alexander Hesler, came into the George Eastman House conservation lab for treatment. This object presented the perfect opportunity to examine innovative treatment options for broken photographs on glass. As a result, many groundbreaking treatment options have been explored. While some of the procedures that were used in the final treatment of this object were already in practice, many new treatment techniques have been developed. Some other treatment options have been explored in the course of this research in the series of case studies. Though there are still many avenues to explore, there is now a better understanding of some of the dynamics of treating photographs on glass.

Part 1. History of photographic processes on glass

Summation of glasses used

The importance of high quality glass as a photographic support was an issue that was revisited many times in the early years of photography. Observations of weeping and color shifting skylights and deteriorated photographs lead photographers to seek out the best glass for their purposes. Patent plate glass was considered the best, as stated by a Frederick Scott Archer in 1854:

“Many pictures have been spoiled, which otherwise would have been good specimens of skill, by the want of due care and attention in the choosing and proper preparation of the glass plates…

Thin patent plate glass is the best kind at present in use, but it has one defect, its color is too green; consequently, it gives an unpleasant tone to positives, which, being looked at through the body of the glass, are affected by it. It would be a great advance if a white glass with the same polish and flatness could be procured.

The next [best] glass to patent plate is flatted crown. It is much cheaper, and very thin; one side of this kind of glass is highly polished, and well adapted for the purpose, but the other side should be avoided; it is rough and gritty to the touch, with a slight haze upon it; the difference between the two sides is easily detected; very often merely passing the finger over it will be sufficient, or examining it in a good light.

Sheet-glass is now made very clear and flat, and is often sold for flatted crown. It is more equally polished on both sides, but it is liable to be specky and rough in places, and the polish generally is more defective; this kind of glass should be avoided if possible. Specks, or scratches of any kind, are liable to produce defects in the picture; consequently, the glass should be examined, to choose the best side previous to covering it with collodion.”

In its pure form glass is a transparent, hard-wearing, essentially inert, strong but brittle, and biologically inactive material that can be formed with very smooth and impervious surfaces. These properties can be modified or changed with the addition of other compounds or heat treatment. The basic ingredients are amorphous silicon dioxide (SiO2), soda (sodium carbonate Na2CO3) or potash, the equivalent potassium compound to lower the melting point, and lime (calcium oxide, CaO) to restore insolubility. The resulting glass contains about 70% silica and is called a soda-lime glass. Soda-lime glasses account for about 90% of manufactured glass.

Cylinder or broad sheet glass, and crown glass were the two processes for making glass for windows up until the 19th century and therefore, the two varieties of glass used in photography during that period.

Broad sheet glass, also known as Cylinder glass was made by blowing molten glass into an elongated balloon shape with a blowpipe. Then, while the glass was still hot, the ends were cut off and the resulting cylinder was split with shears and flattened on an iron plate. The quality of this was poor, with many imperfections and limited size. Crown glass was produced by blowing molten glass was into a "crown" or hollow globe. This was then flattened by reheating and spinning out the bowl-shaped piece of glass (bullion) into a flat disk by centrifugal force, up to 5 or 6 feet in diameter. The glass was then cut to the size required. Because of the manufacturing process, the best and thinnest glass is in a band at the edge of the disk, with the glass becoming thicker and more distorted towards the centre.

Plate glass developed out of the manufacture of broad sheet glass and the need for higher quality glass. The ingredients varied with manufacturer, but they all had special care taken concerning purity. Early plate glass was made from broad sheet glass by laboriously hand grinding and polishing both surfaces. It was later developed into a process whereby molten glass was poured onto a flat table and spread over it to the thickness required, then placed in an annealing oven. After the glass was anneal it was ground with sand a water and polished with powdered emery. Plate glass was of a sufficient quality and size for mirrors and photographic purposes.

Patent Plate Glass evolved from Broad sheet glass. Patent plate glass was lighter and produced from cylinder glass that had been polished via the same method as plate glass. James Timmins Chance was full partner in the Chance Brother’s Glassworks, producers of crown glass, and plate glass by the cylinder process. His first achievement was to design the machinery to grind and polish sheet glass, which made the firm’s glass exceed all others in brilliance and transparency. By May 1841, with the aid of the new machines, the company was turning out more than 4,000 feet of glass per week to meet the enormous demand for the new, patent plate glass. One of the first orders that Chance supervised was 28,000 feet of glass supplied to glaze the Houses of Parliament.

Colored glass, also known as Ruby glass, was produced in a number of ways. Metals could be added to the chemistry to produce vibrant colors: such as gold or copper to produce red or manganese to produce amethyst ruby glasses, both used in the ambrotype processes. Colored glass could also be made by flashing; the application of a thin veneer of colored glass, or by coating a sheet of clear glass with collodion or gelatin containing dye colorants.

Opal glass, also known as Milk glass, is a white, translucent glass used in the production of opalotypes. There were hundreds of formulas for the production of opal glass, but Tin or Zinc oxides (TiO2 or ZnO), lead arsenate [Pb3(AsO4)2) and phosphates were among the most prevalent ingredients used to produce white opaque glassi. There were two varieties of opal glass available: “pot” or “pot metal” and “flashed”. Pot opal is white throughout the body of the glass, while flashed opal glass has a layer of white opal glass “flashed” onto clear sheet glass. “Patent plate opal” glass was produced by J. A. Forrest in the 1860’s[1].

The above, Figure 1. An 1857 advertisement for plate glass. is intended to give the reader an idea of the costs involved with obtaining glass for photographic purposes. The glass in the third column, “black” would also have been called ruby glass, glass that would have been used in the production of ruby ambrotypes (see below). Flattened crown glass was used as cover glasses in ambrotype and opaltype cases because it was thinner than the other glass available. Patent plate, the most expensive glass, was considered the best glass for photograph supports. It had a clarity and perfect surface that allowed for easier coating and better transparency than the polished sheet glass. For more information, please see the appendix, glass production.

History and Technology

Early Research

In 1816, Joseph Nicéphore Niépce (1765-1833) began experimenting on the chemical fixation of photographs made with a camera obscura. The Heliograph (from the Greek helios meaning sun, and graphos meaning writing or drawing). In 1822, Niépce coated a glass plate with a thin layer of Bitumen of Judea dissolved in lavender oil. He exposed it by direct contact under an engraving of Pope Pius VII. The paper bearing the engraving had been oiled to make the paper nearly transparent. Upon exposure to light, the areas of bitumen shaded by the lines of the engraving remained soft and soluble. The plate was then washed in a mixture of oil of lavender and petroleum. The unhardened portions of the bitumen dissolved away, leaving a clear, fine-lined image. Viewed by transmitted light the image was composed of clear lines in the darker field of asphalt.

Niépce also experimented with bitumen on stone, copper, pewter and zinc plates that could actually be inked for printing. His best printing results, in 1826, used an engraving of the Cardinal Georges d'Amboise. He followed the same bitumen of Judea/oil of lavender process but this time employed a pewter plate in place of the glass one.

During his travel to England, Niépce had met, in Paris, Louis Jacques Mandé Daguerre, painter and decor designer, who had a reputation as a camera obscura specialist. Hoping to shorten the 8 hour exposure time of his Heliograph process, Niépce decided in 1829, to associate Daguerre to his research, and to build a camera obscura giving brighter images. This association did not bring any noticeable progress to the bitumen process; on the other hand, the two partners discovered a new photographic process they called the Physautotype.

The photosensitive agent of this process, fine-tuned by Niépce and Daguerre in 1832, was the residue of lavender oil distillation. Lavender oil was heated and evaporated to produce a dry product. Niépce and Daguerre would then dissolve a small amount of this tar in alcohol, and pour the solution on a well-polished silver or glass plate. After the alcohol evaporated, a uniform white deposit remained on the plate. The prepared plate was exposed to light in the camera obscura for about 7 to 8 hours. After exposure, the plate was suspended face down, above a tray holding oil of white petroleum. The fumes of this kerosene were sufficient to develop the image without any further treatment.[2]

This process produces positive images directly, since the white deposit remains on the plate at places that were touched by light, while the kerosene fumes render transparent the zones that were not illuminated. Images on these plates can be seen as positive or negative: if the plate is backed with a black material the image will appear as a positive and, when viewed by transmitted light, as a negative.

Albumen on glass

The next development in glass supported photographs would not come until 12 years later with Sir John Frederick William Herschel’s (1792 – 1871) work. Herschel was a brilliant astronomer, chemist and thinker, who discovered Halley’s Comet and made advances in photography—such as hypo and the cyanotype. His interest in photochemistry provided the missing link in many of photography’s early experiments by virtue of the fact that he shared his knowledge openly and did not seek patents.

Herschel read of Daguerre’s successes with his Daguerreotype process and set out to produce a permanent photograph himself. In 1839, Herschel succeeded in producing three positive/negative photographs on glass (Figure 2). On September 9, 1839, Herschel photographed his father’s 40-foot telescope in Slough, near London. Alexander Stewart Herschel, John Herschel’s son, gave a talk to the Photographic society of London in 1872, after this father’s death, describing the day the three images were taken and the process involved. After the talk, one of the photographs was broken in half and Herschel suggested that it be used for study.[3] The whereabouts of the second plate are unknown, and the third is in the collection of the National Media Museum at Bradford (England). This is the earliest surviving photograph on glass.

In his process, Herschel precipitated a highly diluted solution of sodium chloride and silver nitrate (producing silver chloride) onto a clean glass plate to form a thin coating of silver chloride; a process that took nearly 48 hours. Shortly before exposure, he added more silver nitrate and exposed the plate while it was still wet. The plate was then washed in a dilute chloride solution, then treated with a solution of sodium thiosulfate, which fixed it permanently. The resulting image was a well-defined negative.[4] Herschel went on to suggest that “If then the other side of the glass be well smoked and black varnished – the effect much resembles Daguerreotype being dark on white as in nature and also right and left as in nature and as if on polished silver”. Furthermore, he noted that if the plate were not smoked and varnished, and the silver coating were thickened by galvanization “there seems no reason why impressions could not be taken from it ad infinitum…”[5]

Herschel was modest regarding his findings. In a conversation with Henry Fox Talbot, related by Alexander Stewart Herschel after his father’s death[6], John Herschel was said to have commented upon presenting Talbot with one of his photographs on glass, that the process was ‘but a step’ in the improvement of the photographic process. Talbot replied, after examining the object for a short time, “It is the step of a giant!” Talbot suggested that Herschel call his process the Amphitype (from the Greek for “on both sides”), or perhaps Allotype[7] based on a derivation of the Greek word for “to change”. While Herschel did not wish to market his discovery, he did go on to use the process rather extensively. This process was painstakingly delicate and timeconsuming when compared with other processes of the time. It was practiced and improved upon by a few photographers—such as Robert Hunt and Hippolyte Bayard, who praised the process for its clarity and detail[8].

In 1840, William Henry Fox Talbot conducted some experiments involving albumen on glass fumed with iodine and sensitized with silver nitrate. He first coated the plate with albumen and silver, then after, coating it with a layer of albumen and ferrous iodide, dipped it again in a silver bath. The plate was extremely sensitive and could freeze the image of a rapidly rotating disk that was instantaneously exposed by the light of an electric spark.[9] He patented his modifications of the albumen-on-glass process in 1849 and again in 1851; thereby stymieing the advancement of the process, and any other process involving albumen-on-glass, in England. (He also tried several combinations and variations—including albumen salted with potassium iodide. Evidently those efforts did not have enough success to warrant publication.[10])

John Adams Whipple (1823 – 1891) began his experiments into glass supports for photography in Boston in 1844. With his partner, William B. Jones, he was determined that glass could be a workable support for photographs, as he was very dissatisfied with the imperfections that resulted from the use of paper negatives. After many failed attempts with “…milk [and] various other substances of a gelatinous and albuminous [sic] nature…”[11] he determined that albumen was the most promising binder. When sensitized with silver iodide and fixed with hyposulfite of soda an image was obtained. However, the image was contrasted in the extreme, with almost no middle tones.

Whipple and Jones continued experimenting with this process, but became distracted by Whipple’s work with microscopic daguerreotype images, and in 1847 Niépce de Saint Victor in France announced his albumen process to the world (see below). Being preempted in this manner caused Whipple to scramble for a patent in the United States, but it was not until 1850 that he obtained his patent for the Crystalotype (Patent Number 7,458)[12]. This patent covered the use of glass, or another transparent medium, as the carrier for a binder (he suggests albumen and honey for faster exposures), to make negatives on glass, from which paper or glass prints might be produced. Whipple later used the term crystalotype to cover any process that originated in a photograph on glass (e.g., salt or albumen print made from an albumen negative).

In 1853, Whipple sold the rights to the albumen negative process to James E. McClees of Philadelphia, and graduated to using collodion negatives to produce crystalotypes.[13] The use of the process did not cease with its sale to McClees, who perfected the process and marketed it extensively in the United States and Europe. As late as 1858, the process was the one recommended to amateurs for outdoor photography, and in 1885, Charles Ehrmann gave what is apparently the only recorded description of the process in a lecture to the Photographic Section of the American Institute.[14]

In 1847, Claude Felix Abel Niépce de Saint-Victor (1805 – 1870), a chemist (and cousin of Nicéphore Niépce) introduced the first practical photographic process on glass. In October of that year, Niépce de Saint-Victor published an account of his experiments utilizing starch on glass in the Compte Rendu des Séances de l’Académie des Sciences. The process relied on sensitization with silver iodide and development with hot gallic acid with small amounts of aceto-nitrate of silver. He acknowledged at the end of the article that albumen was a superior binder; while it a required longer exposure time (35 seconds for starch, and 5-15 minutes for albumen) it had highly superior resolution.[15]

Niépce appeared before the Academy of Sciences in Paris to announce his new process, called the Niepceotype, using glass plates coated with an emulsion of potassium iodide suspended in albumen (Figure 3). After exposure, the plate was developed in gallic acid. The process could be done wet, (for a faster exposure), or dry. While the process was slow, with an exposure time of 5 to 15 minutes, the plates had very high resolution and were used for architectural photography and lanternslides. During the French revolution of 1848, rioters entered Niépce de Saint-Victor’s laboratory and destroyed everything. This delayed the adoption of the French process and gave Whipple the opportunity to improve upon his own.

In 1847, Louis Désiré Blanquart-Evrard, a cloth merchant from Lille, France, announced a process similar to Niépce’s albumen-on-glass. He noted that silver-iodized albumen could be exposed wet or dry and introduced the amphitype process, a predecessor to the ambrotype. Blanquart-Evrard underexposed a Niepceotype and placed it upon a dark background. When viewed through the coated side, the product showed as a positive, and from the back of the glass, a negative.[16] The Robertson album in the George Eastman House archives gives splendid examples of prints made from albumen negatives.

At the same time that Whipple was scrambling to patent his albumen-on-glass process, Frederick (1809 – 1879) and William (1807 – 1874) Langenheim of Philadelphia were working on their own method of producing photographs by means of albumenon- glass. While Whipple’s patent applied to the production of paper photographs made from albumen negatives, the Langenheim process applied to the production of positive glass transparencies from albumen negatives.

In 1848, the brothers made positive transparencies using albumen. They copied daguerreotypes by the albumen negative process (Figure 4) and then contact printed onto a second sensitized albumen plate. Then the second plate was developed, fixed and washed, the image was positive when viewed by transmitted light (Figure 5). This final positive image, called the Hyalotype (“hyalo” from the Greek for glass) was applied to the production of Lanternslides and stereographic images, and patented in 1850 by Frederick Langenheim (Figure 6), patent Number 7,784. This patent covered the use of transparent or frosted glass, or any semi-transparent substance, to make a positive upon glass, for viewing with transmitted light, standardized at 3.5" x 4". Eventually, the brothers also produced stereoscopic transparencies on glass: in 1860, Frederick Langenheim was listed as "stereoscopes", at 722 Chestnut Street,[17] and in their 1861 catalogue they are called the American Stereoscopic Company.

Hyalotypes were the first photographically based lanternslides that were often tinted with transparent colors to enhance the effect on the screen. Before the Hyalotype, lanternslides were merely hand-painted images on glass. By using a negative to print onto another sheet of glass, the Langenheims were able to create a transparent positive image, suitable for projection (Figure 7). Used in "Magic Lanterns" the image was projected onto a screen. This new method became extremely popular and the Langenheims’ business increased after their process won a medal at the 1851 Crystal Palace Exposition in London.

Many other companies followed suit and began producing Lantern slides by the albumen on glass process, and after a short period, switched to wet-collodion plates. The introduction of dry plate processes, as well as mass-produced lantern slide kits, made the slides easier for amateur photographers to produce and also made them more accessible to schools and universities.[18]

There were two methods for producing the positive transparencies: either by contact printing or in-camera. Contact printing required that the negative be the same size as the desired transparency (3.5 x 4 inches). If this were not possible, the in-camera method would be used: the negative and the glass were both placed in a camera with a long bed and bellows and printing was done by exposure to light. After development and drying, the plate could be hand-colored using transparent tints (Figure 8). The method of mounting preferred by Langenheim was to cut the positive and the cover glass into a circle and insert this into a wooden frame of a size to fit the lantern. A more general method of mounting was to cut the positive and cover glass to square, with a spacer in between, and fasten the edges with thin strips of black muslin or paper, using bookbinder’s flour paste[19]. The slide could then be inserted into in a lanternslide projector and viewed on a flat, light colored surface. The light source in the first projectors were oil lamps, and by 1870 limelight was produced by burning oxygen and hydrogen on a pellet of lime.[20] In the 1890’s the carbon arc lamp and then electric light was used.

In 1851, Claude-Marie Ferrier (1811 – 1889), an early French photographer who recorded the items shown at the 1851 Crystal Palace Exhibition, introduced a modification of the Langenheims Hyalotype process to Paris: stereoscopic albumen-onglass positives. Ferrier went into partnership with Charles Soulier and in 1859 they opened a business in Paris to sell albumen-on-glass stereo views, published under the name “Ferrier et Soulier”. They went on to become among the leading landscape photographers in Europe and by 1864 their catalogue offered a large selection of views of Paris, France, and foreign countries including Norway, Russia and Japan.[21]

Figure 9, Saint Eustache in Paris, by Ferrier and Soulier, contains an interesting illustration as to how a stereo transparency was taken. Figures b and c are of the clock in the right central edges of the two images in figure a. Figure b was taken at 11:25 am and figure c was taken at 11:37 am: 12 minutes apart. These observations show that the plate was produced by making the exposure on the right (b), then moving the camera and taking the second exposure on the left (c), 12 minutes later. The fact that the second exposure is slightly out of focus is because the camera was jarred during the sifting of the camera and not refocused. In addition, the figures on the street are different, a carriage has disappeared and people have congregated between the two exposures. By the 1910’s, stereo photographs were taken with a duel lens camera that allowed both exposures to be taken at the same time.

In 1854, the Langenheims began producing stereo transparencies by their albumen process. The plates were mounted with a ground glass backing and often featured subtle hand tinting. Single sides were made available for use as lanternslides.

Woodburytype, Carbon and collodion bases were also used in the production of lanternslides (Figure 10) and stereoscopic plates. The three processes can be difficult to distinguish from each other.

The Carbon process had many fathers. It was theorized by Alphonse Louis Poitevin (1819 – 1892), and improved upon by many others in the following years, most notably John Pouncy (ca.1820 – 1894), C.J. Burnett, Adolphe Fargier and (Sir) Joseph William Swan (1828 – 1914). In 1855, Poitevin patented his observations of the effect of light upon chromated gelatin mixed with pigment, titled “Improved photographic engraving” (BP No.2816)[22]. J. Pouncy produced the first carbon prints, and patented the process, titled “Improvements in the production of Photographic pictures” in 1858 (BP No. 780)[23]. These early versions were unsatisfactory in their poor rendition of half-tones, and J.C. Burnett and A. Fargier made further improvements in 1858 and 1860, respectively. However, it was J.W. Swan’s 1864 patented carbon tissue, titled “Improvements in photography” (BP No.503)[24], which made the process practical for photographers.[25]

A carbon pigment is suspended in gelatin and sensitized with potassium bichromate, which hardens upon exposure to light. After exposure of the sensitized carbon under a negative, the portions that have not been hardened were washed away in a warm water bath, resulting in a positive image. The Carbon process (Figure 11) produced a continuous tone image because of the proportional hardening of the potassium bichromate upon exposure; the gelatin hardened from the top down, with the degree of exposure determining the depth of hardening. This “tissue” (the common tern for the film of emulsion on the paper) was then transferred to another medium such as, in the case of lanternslides and stereoscopic plates, glass, and washed in warm water to remove the unhardened gelatin. The early experiments of Poitevin and Pouncy produced such poor half tones because they did not do this transfer and were therefore removing the unhardened portions of gelatin through the intermediate areas. The image in this case would be laterally reversed. To remedy this, another transfer could be done onto a third and final support. The final image had thicker and thinner areas of pigmented gelatin, depending upon the degree of exposure, and therefore a relief, that aids in separating this process from other binders, such as collodion.

Suppliers such as the Autotype Company in England supplied 30 different colors of tissue.

Another process used in the production of Lanternslides was patented by Alexander Melville Clark, in communication with Claude Léon Lambert in 1874 (BP no.3633)[26]. The patent described ‘Improvements in Producing Carbon Photographs', and included details of his Contretype process. In this process, a copy negative is produced by coating a glass plate with gelatin and sensitizing it with potassium bichromate. After drying, it is then exposed under a negative. After exposure, the plate is soaked in India ink—any unhardened sections of the gelatin absorb the color.[27] The Woodburytype process was patented by Walter Bentley Woodbury (1834 – 1885) in 1864 (BP No. 2338) and perfected in 1866 (BP No.1918)[28]. In this photomechanical process, based on Poitevin’s carbon process, an intaglio lead mold is made from a relief image (matrix) that has been obtained with bichromated (hardened) gelatin, in a hydraulic press, under very high pressure. This mold is then inked with colored gelatin and the image printed onto the final support. A modification of the process , published later, BP No.3760, 1879[29], was called the Stannotype. It did not require the expensive hydraulic press. Woodbury himself gave perhaps the most concise description of the Woodburytype process:

“The production of pictures, wither [sic] on white paper, upon glass as transparencies, opal, etc., by this method of printing is based on the principle that layers of any semi-transparent material seen against a light ground produce different degrees of light and shade, according to their thickness, as the carbon process, for example.”[30]

The salient feature of the Woodburytype process was that it made relatively simple the production of glass lantern slides of very high quality in large quantities. Once the matrix was formed, copies could be created by inking the mold with colored gelatin and printing onto another support, rather than having to work with the chemistries and slow printing times involved with albumen printing, or the grain of a half-tone screen. In the 1890’s the process was replaced by lower quality, but also lower cost, photomechanical reproductions.

Wet-plate Collodion on Glass

Frederick Scott Archer (1813 – 1857), the inventor of the collodion wet-plate process, was orphaned as a child and apprenticed out to a bullion dealer as a boy. He eventually became a coin appraiser, with a special interest in the portraiture involved. This led him to sculpture and then photography. Intending to improve the collotype printing process[31] (collo, from the Greek word for glue) by using collodion as a binder, Archer developed the wet collodion process. He initially intended to use glass as a temporary support for transferring collodion onto paper. In this process, a glass plate is coated with iodized collodion and exposed while still wet, then developed in pyrogallic acid. Dr. Hugh W. Diamond and Morgan Brown were close confidants of Archer and accompanied him on many of his photographic outings. In an 1875 article about the life of Archer, Brown contributed notes concerning his experiences with the man:

“My desire to know something of photography… induced Dr. Diamond to ask Archer to meet me at Wandsworth Asylum on Michaelmas Day, 1850. There Archer brought some collodion in a bottle and some solution of silver… [Archer] poured the collodion on a piece of glass about three by four inches, sensitized it in the nitrate of silver… put a picture of a house in front on it, exposed it, and developed it into a picture, the film being detached from the glass, and subsequently placed it for preservation between two pieces of glass.”[32]

Archer also made a collodion picture in a camera that day, described by Brown as a “faint image of a tree”, but Brown admits to having lost the images or given them to Dr. Diamond. At that point, Archer did not intend to create a new process. He desired to improve upon the calotype process by using collodion, but he could not get the collodion to stick to the paper. That was not accomplished until the invention of the porcelain, and subsequent Leptographic papers. Porcelain papers had a sub coating of white clay or baryta mixed with gelatin, which was then fed through heavy polished metal rollers to impart a china-like finish. In 1870 Jean Laurent and Jose Martinez in Madrid, Spain created leptographic papers by coating porcelain paper with collodion-chloride emulsions.

Archer apparently spent the autumn of 1850 creating collodion plates, honing his process. In March of 1851, Archer published his findings in The Chemist, where he discussed the advantages of collodion and offered detailed instructions on the process. In 1854, he published his manual on the process The Collodion Process on glass. In it, he discusses the varieties of glass and how to choose the proper type. Gustave le Gray and RJ Bingham both made claims to the invention of the process, but never published workable formulas.

Regardless, Archer was the first to publish a workable formula and make it available to the public. Figure 12 is a print from one of Archer’s series of negatives taken at Kenilworth Castle in 1851.

Archer also established a collodion positive on glass, or alabastrine, process in 1851 (later known as the ambrotype process), in collaboration with Peter Witkins Fry (1772 - 1860), a lawyer, amateur photographer and a founding Council member of the Photographic Society of London.. Coincidentally, Fry was the solicitor for the defense in the patent infringement case Talbot vs. Laroche in 1854[33] that contended that the collodion process infringed upon Talbot’s calotype patent. The process quickly supplanted the daguerreotype as the portrait method of choice. It was inexpensive and therefore, available to the masses, not just the moneyed class. By 1852, photographers in London were promoting the process as something “any person can produce in a few seconds, at a trifling expense, truly life-like portraits.”[34] The plate sizes followed the Daguerreotype designations.[35]

Designation Inches Centimeters
Whole 6 1/2 x 8 1/2 16.5 x 21.5
Half 4 1/4 x 6 1/2 10.5 x 16.5
Quarter 3 1/4 x 4 1/4 8.3 x 10.5
One-sixth 2 3/4 x 3 1/4 7.0 x 8.3
One-eighth 2 1/8 x 3 1/4 5.3 x 8.3
One-sixteenth 1 5/8 x 2 1/8 4.0 x 5.3

Collodion positives on glass were made by underexposing wet plate collodion negatives. The silver particles of collodion plates are extremely small, and therefore are seen in reflected light as a brown color. Archer’s alabastrines were developed in Pyrogallic acid and were very dark. They required bleaching with mercuric chloride to whiten the highlights. Later, collodion positives were developed with iron sulfate, which produced a light gray or creamy tan image, that did not require bleaching. When backed with a black material such as fabric, paper or a painted on carbon or asphalt paint historically called ‘Japanning’, the strongest milky-brown tones of the plates correspond to the highlight areas of the image and the darkest tones are clear glass. The collodion side of the plate would also be varnished with a mixture of a gum or resin, such as sandarac, shellac or Canada balsam, in a solvent, such as water, alcohol, or turpentine. There were also many commercially available varnishes for photographic use. Sometimes light tinting with powdered pigments would be applied on the binder side of the plate to the cheeks of the sitter, or even the clothing and scenery (see Figure 20).

The finished plate would then be covered with an equal sized piece of clear crown glass, with spacers added so that the two were not in direct contact. This is commonly called a double-glass ambrotype (Figure 14). The glass side of the plate would be backed with black material, such as paper or fabric, or a black japanning paint, consisting of asphalt or carbon in a binder, would be applied directly to the glass. A brass preserver would be wrapped around the sandwich to make a package. All this would then be placed in a case ( Figure 16). There were variations on the construction of the image pack as well: if the photographer decided not to apply the japanning to the image plate, he could apply it to a second sheet of backing glass. These ambrotypes are commonly referred to as triple-glass ambrotypes (Figure 15). A single-glass ambrotype would not have a separate cover glass and the plate was simply inverted in the package so that the glass side of the image plate acts as the outer surface (Figure 13). The image plate could be japanned on the collodion side of the plate; the plate might not be varnished, a lack that inevitably lead to tarnishing and image loss; or black paper may have been glued directly to the back of the plate to create the positive.

When the collodion positive process hit the market in the mid-1850’s it was quickly accepted by the public. The faster exposure times, coupled with the ease of viewing, allowed the process to replace the Daguerreotype as the popular studio portrait technique. At this time, the process was recognized by a number of different names: collodion-positive, daguerreotype-on-glass, daguerreotype-without-reflection, and in Europe, either verreotypes (verre is the French word for glass, from the Latin vitrum), or amphitype (from Greek, for amphi meaning on both sides).

The term ambrotype first appears in James Ambrose (Anson) Cutting’s (- 1865) 1854 English patent (No.1638)[36]. Legend has it that the name ambrotype came from Cutting’s middle name, but, it is known that he had his middle name changed from Anson to Ambrose when he patented the process, to make the name seem serendipitous[37]. His particular method of production was to seal the collodion binder against another sheet of glass with Canada Balsam, a process that had been known in the manufacture of microscopic slides. (Figure 17) To accomplish this, a line of heated Canada balsam was laid along one edge of the cover glass and the image plate was aligned, then slowly laid down, pressing out the excess balsam and air bubbles. This package would then be sealed with paper tape around the perimeter and fitted into a case. If the name ‘ambrotype’ were to be taken literally (ambrotos, from the Greek for imperishable), then this method produces the only true ambrotype. The sealing of the image binder against another sheet of glass makes the image highly resistant to adverse atmospheric and environmental conditions.

An interesting feature of the Cutting ambrotype is that it inspired the creation of a different variety of case. Figure 18 is an example of a ‘double hinged’ case. The sealed nature of the ambrotype serves to protect the image binder to such a degree that this case was created, presumably, to allow the viewer to see a proper backwards, or alternatively, a transparent view of the plate. It is interesting to note that this case allowed for two views of the sitter: one that showed the sitter as he saw himself in a mirror (the only way people saw themselves at the time), and therefore a more familiar view and another, “proper view”, that showed how the rest of the world saw the sitter. It is uncertain where these cases originated, but the photographer Mathew Brady produced so many of them that some dealers describe them as ‘Brady cases’. Most of the cases were constructed of leather-covered wood, with finger joints for added stability, and others were made with a steel frame. These cases also required a special kind of double preserver to hold the plate-package together while maintaining the aesthetics of both sides of the package (Figure 18b). Smaller plate-packages were held into the case with the pinchpad, while larger packages required metal tabs to be built into the frame.

The ‘Relievo’ portraits were introduced in England in 1857 by Thomas C. Lawrence, a Greenwich photographer. [38] The ‘Relievo’ ambrotype was based on the relief effect that was achieved by the layering of the image plate over another image or background. The structure of a relievo ambrotype could have been single, double or triple (see above), depending on the style. Many relievo ambrotypes are very simple, with merely a piece of white or light colored card (Figure 19b), or other light material such as foil (Figure 21), placed behind the sitter at the time of exposure. The most simple relievo ambrotype was made by placing the subject in front of a white background, to give an even light tone (Figure 20) on the final plate, and then applying blacking behind the sitter on the image (Figure 19b). Other methods included placing the sitter in front of a black background, to give no exposure behind the sitter; or to make the ambrotype in the usual way, and then scraping away the background (Figure 21).

Figure 21 is an example of a more complex relievo ambrotype in which a portion of the primary image has been posed on a background. The tree behind the figure was on a second ambrotype layered behind the first, taken from the sketch on the table. The image plate is backed with blacking behind the figure. A secondary image plate or other material is placed behind the image plate and this fact is concealed by the brass mat. Spacers, usually made of cardstock, separated the two from each other.

The Sphereotype was patented by Albert Bisbee in conjunction with Yearless Day in 1856 (US patent #14,946). The process involved making the border of the image (ambrotype) transparent, and placing the mat behind the image plate with the advantage of protecting the mat and “making the picture appear more round, causing an illusion, as thought the picture or image was suspended in the atmosphere clear from the background.” This was accomplished by placing a board inside the camera of “an aperture of any desired pattern that we wish the edges of the picture to have” [39], leaving the shaded portion of the plate clear (Figure 23c). After processing, blacking is applied behind the figure only (Figure 23b), and the mat is placed behind the image plate in the plate-package (Figure 24).

Figure 23 are of the same sitter, Mr. Charles P. Smiley of San Francisco, and taken by Robert H. Vance, in 1857. The Sphereotype (sphere, relating to the circular image area on the plate) in Figure 23 has the look of a Sphereotype, but it is not a true one. This plate was probably taken at the same time as the above Cutting ambrotype of Figure 9, but then the emulsion was scraped away to give a pseudo-relievo-Sphereotype look, which was rather popular at the time. A true Sphereotype would have a more indistinct border around the image area. This is being pointed out so that the reader will understand that studios did not always specialize in one type of portrait: they usually offered a variety to suit the sitter’s tastes. Another variation of the relievo ambrotype was a rather American permutation: the sitter was photographed against a white background and backed with blacking behind the sitter to give a small relief effect and a very even background.

Another variation of the ambrotype process is the ruby-glass-ambrotype or rubitype. The name was taken from the dark glass used as a base for the collodion image. Although the word ‘ruby’, implying red (Figure 25), was used, and was indeed the most commonly used color, the color of the glass could be of any dark hue: dark red, blue, green, purple (sometimes called amethyst), orange, or brown. Ambrotypes on ruby glass were considered higher-end photographs. This was partly because of the cost involved in obtaining the glass , but also because the dark glass support produced blacker shadows in the final image, obviating the need for dark paper backing or japanning, which were subject to deterioration or flaking . Companies that sold the glass to photographers would list it as ‘black’ glass and attached a higher price to the material. Figure 1, on page 1, depicts a 1857 advertisement[40]. Note that the ‘black’ glass is second in cost only to patent plate.

As with any photographic discovery, there are imitators and innovaters. The Cutting ambrotype had many imitators. Some that used inferior materials or colored glass as a backing, and others that created what appeared to be an entirely new process. The Chromo-crystal was introduced to London by Thomas Skaife in a letter to the Brighton Herald in 1859.[41] A small collodion plate was exposed in Skaife’s patented (BP No. 1373) Pistolgraph camera, with his patented (BP No. 2939) flash mechanism. The resulting plate measured approximately 6.7 x 3.2 cm, with an oval image area measuring approximately 4 x 3 cm (see Figure 27). This would then be cemented with Canada balsam to a piece of ruby glass, approximating the image area, and “baked…over a lamp until the two glasses are so united as not to be separable without breaking”.[42] Once finished the “gem” could be trimmed to between “1 1/2 to 3/8 of an inch in diameter after they are trimmed by the lapidary. They are the neatest and bestexecuted portraits… suitable for mounting in bracelets, brooches, pins or rings”[43] (Figure 26). Skaife claimed that the sealing with balsam and subsequent heating was the best way to preserve the image, even going so far as to claim it could not be damaged. This attribute is probably more likely a function of the physics involved in separating two small pieces of glass that are well cemented together, rather than the heating.

A more popular use for the tiny plates was to print them onto small calling cards. These photographs were called pistolgrams after his Pistolgraph camera. The tiny size of the image plate and camera lens resulted in “instantaneous” photographs (about 1/15 sec. exposure), and the technique was marketed for images of babies and pets. Skaife was also known to take portraits of equestrians in Hyde Park “in all phases of motion”[44], and exhibit them in his near-by Baker Street studio in London.

Opaltypes, also known as Opalotypes or Milk-glass positives, were produced from 1860 until the 1940’s. The process was patented by Joseph Glover and John Bold the younger in 1857 (BP No. 501). This patent covered the use of “Enamelled glass, minerals or other suitable mineral substances” that were washed first with fluoric acid to etch the surface and prepare it to receive “the collodion or other sensitive substance”, and exposed through a negative. They went on to describe how the finished photograph could then be tinted (Figure 28) with “water colors, oil colors, dry colors, and varnish colors.” [45]Other variations on the process included, grinding down the glass slightly with fine emery powder, or the application of a matte varnish, to increase the adhesion of the binder layer to the glass[46]. The light sensitive binder could be gelatin, albumen, collodion, or carbon transfer—the point being that the opaltype took advantage of all of the variations of the various binders. Very often, opaltypes would be housed in brass frames or cases similar to those used to house ambrotypes (Figure 29).

The term “opaltype” became common for the process by mid-1860, although, over the years, some variations on the process and interesting nomenclature were introduced. In 1864, the British Journal of Photography reported experiments by Frederick Augustus Wenderoth, which involved the application of albumen chloride binder to ground pot-opal glass. Wenderoth called his process the Toovytype.[47] The same article also mentions a William Helsby and his collodion iodide variant called, the Helioartistotypia, patented in 1865[48] (BP No. 12).[49]

Vitrified photographs on glass are still being produced in some regions of Europe for headstones and other decorative purposes. These permanent photographs have had many new developments in the past 150 years. The roots of this process however, lie in James A. Forrest’s experiments. He based his work on burnt-in photographs on the observations, made in 1280[50], that when salts of silver are laid upon glass and exposed to 750°C a transparent yellow tone will result. In Forrest’s process, a collodion positive on glass was coated with a flux mixture of very finely ground flint glass, pearl ash, borax, red lead and chloride of sodium. When dry, this is exposed to 750°C in a kiln for about three minutes. He suggested the use of porcelain, opal or clear glass. At a meeting of the Liverpool Photographic Society in 1857, Forrest showed specimens from his experiments. These consisted of photographs seen by reflected light with a dark background, and transparencies for hall lamps and windows. [51]

In 1862, Ferdinand Jean Joubert de la Ferté, a French engraver, read a paper at the Meeting of the Photographic Society in London in which he discounted Forrest’s process as too delicate and difficult to reproduce. He stated that in most cases “...although some portion of the silver was retained in a yellow tint on the glass when taken out of the kiln, the greater portion of the photograph has disappeared: for the organic substance of the collodion was burnt off, and left no trace on the glass in many instances.”[52]

Joubert called his process enamel photography and patented it in 1860 (BP No.149).[53] He coated a piece of crown or “flatted” (cylinder) glass with a mixture of: “bichromate of ammonia in the proportion of five parts, honey and albumen three parts each, well mixed together, and thinned with from twenty to thirty parts of distilled water, the whole carefully filtered before using it.” He advised that this mixture be prepared in a darkened room or under yellow light “so that the sensitiveness of the solution may not be diminished or destroyed”. After drying, this was placed in contact with a diapositive, such as a positive photograph on clear glass or waxed paper, in a printing frame. After exposure, a “faintly indicated” negative was be visible in the sticky coating. This was then brushed with enamel color until the subject appeared as a positive. It was then fixed in an alcohol and acetic acid wash, and submersed in a pan of clean water “and left until the chromic solution has dissolved off, and nothing remains except the enamel color on the glass”. The plate was then dried and fired in a kiln. [54]

Joubert was also the first to produce good results from Poitevin’s collotype process. The process was based on the observation that when stone, metal or glass coated with bichromated gelatin , is exposed under a negative and then exposed to water, a greasy substance is formed in proportion to the areas exposed to light. This would then be used to make photographic prints. Joubert called his prints “Phototypes”. He never published his version of the process however, and it never came into common use.

Preserved and Dry Plate Collodion on Glass

A hurdle that photographers needed to cross in collodion photography was the inconvenience of working with the wet-plates. It was cumbersome to have to carry your darkroom around and process immediately after sensitization. Photographers desired a method of preserving the sensitivity of the plates without having to coat, sensitize and develop in the field.

Preserved Collodion Plates

In 1854, George Shadbolt (1830 – 1901) partially succeeded in solving this problem with the introduction of his honey process (honey diluted with distilled water) or basically, the discovery of the “Sugar and water” preservative process.[55] The sugar solution acts as a humectant that keeps the sensitized collodion moist and therefore, extends its sensitivity[56]. This process had many permutations such as, the “Sweet Wort process” the “glycerine process”, the “Raspberry vinegar” process, and finally, the Oxymel process.

An early version of this process, introduced in 1856 by John Dillwyn Llewelyn (1810 – 1882), kept sensitized collodion moist by coating the plates with a medical tonic of honey and vinegar called Oxymel. Plates coated in this manner would retain their qualities for months; however, at the expense of sensitivity.[57] Figure 30, is from a Photographic Exchange Club album in the George Eastman House collection and was taken by Llewelyn with his Oxymel process. The accompanying inscription states: "And in the weedy moat, the heron fond of solitude alighted. The moping heron motionless and stiff, That on a stone as silently and stilly stood, an apparent sentinel, as if To guard the water-lily… Taken by the Oxymel process, June, 1856; weather dull; exposure twenty minutes; developed with Pyrogallic Acid.” It may be surmised that the Heron “in its natural surroundings” was in fact a stuffed bird, placed in the pond. Nevertheless, the intention of demonstrating the versatility of the process and its possible outdoor, landscape-photography applications, was accomplished.

One of the most popular preserved collodion processes was the Taupenot Process, introduced by Dr. J. M. Taupenot (1824 – 1856) in 1855, the first practical dry collodionalbumen process[58]. In this process a collodion plate was prepared using the Tannin Process, introduced by Major Russell in the mid 1850’s, whereby the collodion plate is washed clean of excess silver while wet, coated with a solution of tannic acid, and allowed to dry. In Russell’s process, the coating of tannic acid allowed the plate to be kept in dark storage for months before exposure. Taupenot’s process called for an additional coating of iodized albumen and another coating of silver nitrate (thus providing two sensitive layers). This first dry plate process could be stored for several weeks before exposure. The only drawback to these processes was a greatly increased exposure time (about 6 times longer than the wet collodion process, depending on the storage time).[59]

Dry Collodion Plates

The preserved collodion process can be divided into two categories: preserved moist, as previously described, or dry. In both of these processes, a wet collodion plate is sensitized in a silver solution then washed in water, before coating the surface with a humectant as in the case of the Oxymel process, or a siccative, as used in the Tannin process. The Tannin plate had the same sensitivity as an Oxymel plate, but the collodion film was completely dry.

Collodion Emulsion

The separate silver solution was dispensed with when the collodion emulsion process was introduced. Collodion emulsion was made by combining the collodion binder , the halide (iodide, bromide or chloride) and the silver together in the same bottle prior to coating the plate. Collodion emulsions were made as washed or unwashed. Unwashed collodio-chloride emulsions were made for printing-out plates (opaltypes and lantern slides) and printing papers. Washed emulsions were made specifically for negatives and positives on glass.

A “washed emulsion” is one that has been washed of an unwanted compound formed during its making, before the glass plate is coated. When silver is added to the salted collodion, double decomposition occurs whereby the light sensitive salts are formed. For example, when an emulsion is made with potassium bromide and silver nitrate, silver bromide and potassium nitrate are created. While the silver nitrate is required for photosensitivity, the potassium nitrate is not and is removed in a washing step. If it were not removed, it would crystallize and spoil the plate.

Collodion emulsions were washed by pouring the sensitized emulsion into water in a steady stream; this would produce strings of emulsion, rather like spaghetti. This pellicle was then washed for several hours. When the washing was complete, the excess water was squeezed out and the sensitized emulsion could be stored until needed. To emulsify further the sensitized pellicle, equal parts of ether and alcohol were used to dissolve the emulsion, and the plate could then be sensitized.

There is no clear division between collodion and gelatin-glass plate photography: there were many mixed binder processes from 1870 until the turn of the century, and there were many mixed-binder variations on the collodion process available during the collodion era.

Dr. Richard Hill Norris (1831 – 1916) of England, patented a Collodion dry plate process involving gelatin in 1856 (BP No. 2064)[60]. Hill Norris was the first to realize that an important function of the preservative coating on a collodion dry plate was to fill up the pores of the collodion while they were still wet.[61] This was accomplished by pouring liquid gelatin, albumen, or other similar substance over the wet collodion. Hill Norris patented these plates in September 1856 and went on to manufacture them commercially. Norris Hill’s plates were so popular with amateur photographers between 1856 and 1866, that he founded the Patent Dry Collodion Plate Company in Birmingham in 1858. Norris also went on to improve the process, introducing his ‘Extra Quick Dry Plates’ in 1860.

Gelatin on Glass

The division of washed and unwashed collodion plates can also be applied to gelatin binders. In the washed gelatin emulsion process, a suspension of Silver nitrate, Potassium Bromide and Potassium Iodide is made in a gelatin binder (Figure 31) and allowed to solidify (Figure 32). Once set, the emulsion is “noodled” with a ricer or colander (Figure 33). In the 19th century a piece of open weave canvas would be used to create noodles to make as much surface area as possible for washing.

Noodling and washing is done to remove the excess nitrates and potassium from the Silver nitrate, the Potassium bromide, and the Potassium iodide that was added during the concocting process, leading to Potassium nitrate that will affect the emulsion adversely. Using cold water, so the gelatin noodles do not dissolve, the emulsion is washed for about 15 minutes, removing the Potassium nitrate, which will cause fog and reduce filament size if left in the emulsion.

Chloride and Bromide are two of the three halides used in photography (the third being Iodide, the predominant halide in all of the in-camera processes used prior to gelatin plates). Silver chloride was the light sensitive solution used in early printing out processes (POP), such as albumen, collodion chloride and gelatin chloride papers and plates. A printing out process is one that produces an image as the exposure is done, since it converts to gray-black metallic Ag via photo-reduction. Silver bromide is the most sensitive of the silver halides and is found in the developing out processes (DOP). A developed out process requires development of the invisible “latent image”.

By the late 1870’s, the preserved collodion processes, and gelatin and collodion emulsions, were being used by advanced amateurs to take photographs without having to take the darkroom into the field. One discovery that made this possible was that as the percent of Bromide was increased the sensitivity of the plates increased, making faster exposures possible (Figure 34). Another advancement that allowed for faster exposure was the progression of alkaline chemical development from physical development. Before the 1870’s all development in photography was physical. Acid was used as a restrainer for development and excess or “free” Silver nitrate was required for the image reaction to occur. The silver particles produced by physical development are tiny, compared to chemically developed silver, and have a distinctive color. Chemical development uses an alkaline and no free silver is required. The result is larger, filamentary silver particles that have a cooler tone, and are much more sensitive, resulting in a faster exposure. The earliest experimental gelatin processes were iodide based and required acid development.

Richard Leach Maddox (1816 – 1902), a physician in London, discovered Silver bromide emulsion. In an article in the British Journal of Photography on 8 September 1871, he suggested a process whereby the sensitizing chemicals could be coated on a glass plate in a gelatin emulsion, instead of wet collodion. He described how a gelatin emulsion was formed with nitric acid, hydrochloric acid, cadmium bromide and silver nitrate. This was coated upon a glass plate, exposed, and physically developed in a solution of pyrogallic acid and silver nitrate. The resulting images were “small, delicate, completely detailed brown negatives”[62]. This was the first commercially viable gelatin emulsion. Maddox was a physician and experimented in photography as a hobby. He had freely made his ideas known, and never patented the process[63] and as consequence, John Burgess and Richard Kennet were able to introduce their refinements in 1873.

In 1878, Charles Harper Bennet, and others, made the first gelatin dry plates for sale on the open market, a revolutionary advance in the science of photography. Charles Bennet discovered a method of hardening the emulsion, making it more resistant to friction in 1873. This was discovered by cooking (prolonged heating) the gelatin emulsion so that the sensitivity could be greatly increased.

The Orotone, also known as D’Oroton (French), Dorotone, goldtone, or Curtistone, is a thin (underexposed) positive image on glass, often with a silver gelatin emulsion and made by contact printing the original negative. The process was prominent from the late 1880’s until the 1920’s. The use of gold backing was a common specialty practice and every photographer who used it had his own recipe, in particular, the photographer Edward Sheriff Curtis[64] (Figure 35.). Curtis’ Orotones were particularly luminous and the backing material more stable than most[65]; therefore, he is credited with perfecting the process in 1916. Curtis’ process consisted of backing a gelatin on glass positive with a mixture of banana oil and gold dust. Due to the expense of gold, Curtis developed a technique that substituted brass for gold, and created the "Curtis-tone" process, also known as the Doretype process. These plates were usually housed in special ornate frames.

Colour processes

The Lippman process, introduced by Gabriel Lippman (1845 – 1921) in 1891, is a natural color plate that relies on interference. It is exposed backwards (thru the glass): just prior to exposure, Mercury is poured on the back of the plate holder, in contact with a fine-grain silver bromide on glass. This forms a mirror and light bounces around in the camera, re-exposing the plate. The final plate looks like a dense negative when viewed by transmitted light, and a color image (Figure 36) when viewed by reflected light and at a certain angle. The process was delicate to perform and difficult to view and did not gain widespread popularity.

There were many color screen processes. The first primary color screen process was the Joly process, patented in 1895 by Charles Jasper Joly (1864 – 1906). In this process, an orthochromatic gelatin plate is exposed through a screen of alternating lines of red, green and blue-violet (Figure 37). After development, the plate is then bound with another screen of complimentary lines. When viewed by transmitted light, a color image is seen. The process was not very practical and while a color image, it was dark because of the diffusing filter. This process relied on two plates: one with ruled lines of gelatin with dye interface that had a critical alignment. These plates would lose their colour with differing expansion rates of the gelatin layers or glass deterioration, as seen in the large parrot below.

The first popular color process was the Autochrome process, patented in 1903 (FR.Pat.No. 339,223, 1903) by Auguste (1864 – 1948) and Louis (1862 – 1954) Lumière in France (patented in America, June 5,1906 (No.822,532)), and marketed in 1907. This process has an integral layered structure that cannot be separated. Therefor many of these plates survive today. The Autochrome (Figure 40) is an additive color 'screen-plate' process: the media contains a glass plate, overlaying random mosaic of microscopic grains of potato starch dyed red, green and blue, with lampblack filling the space between grains (Figure 39). This screen of grains worked as a light filter to interpret the scene when the light passed through them exposing a black and white, panchromatic silver halide emulsion. Glass (the plates were available in all standard sizes) was coated with liquid pitch mixed with a small percentage of beeswax (to help keep it "tacky") then the prepared grain was dusted on and manipulated with a mechanized stylus. By this very action, the resultant screen was random in nature. In order to produce no exposure on the rest of the plate, not masked with the colored starch grains, it was necessary to fill the spaces between the irregularly shaped grains. Lampblack was used as filler, applied by way of a special machine.

Face mounted prints

Throughout the history of photography there have always been the “Obscurotypes”[66], the processes that do not fit comfortably into any one category. The face-mounted prints that were made throughout the history of glass-supported photographs often fall into the obscurotype realm: they come in all shapes and sizes, and are mounted to a variety of materials, usually glass. The following is an attempt to categorize some of the most commonly found face-mounted prints.

The American Ivorytype was introduced by F.A. Wenderoth in 1859, consists of a salt print that has been hand-tinted and face-mounted to glass, treated with wax or rosin to make transparent and hand coloured (Figure 41). Sometimes, a second piece of glass or paper backs the image with additional colouring. A similar process, called the Eburnum process, was published in the Photographic News, on May 15 in 1865 and described by J.M. Burgess of Norwich, involved transferring a carbon or collodion binder to a sheet of glass and backed with a zinc-oxide and gelatin mixture to give the impression an ivory backing.

The Crystoleum (Figure 42) process was popular from the 1880’s until the 1910’s, and was usually a albumen print face-mounted to convex glass with gum or paste. The paper is then rubbed away with sandpaper until the emulsion layer is exposed. What was left of the paper was made translucent, if needed, with a dry oil, wax or varnish. The fine details were then painted on the back of the photograph, a second piece of convex glass that has been broadly coloured is layered behind the image glass, and the package is bound with a paper backing. There were some prints produced that did not have any colouring and merely consisted of the print face-mounted to a sheet of convex glass.

Identification Key

How to use the key:

When the used must choose one of two alternatives, a key is said to be dichotomous, and this is the type used here. Let us suppose that you have the photograph illustrated below, in reflected and transmitted light, in front of you. Turn to the next page and read the two alternatives offered at No.1. You will see at once that the photograph is not face mounted, and you are directed to No. 3. The photograph is not color, so you are directed to No. 6. At No.6 it is evident that the glass support is not clear, and this brings you to No. 7. The glass is not white, and this is the end of the trail, the photograph illustrated is a ruby ambrotype.

There are variations on all of these processes and this dichotomous key is meant to be a guide in the identification of glass supported photographs. Further, there is a short definitions section on page --- that will direct the reader to the area within the Process history section.

Ambrotype – a collodion positive on glass. May be housed in a case with black backing varnish or other material behind the plate.

Amphitype (Herschel) – A binderless precipitated silver on glass process. Extremely rare.

Autochrome – an additive color screen process formed with a random array of red, blue and green dyed potato starch particles.

Carbon – A pigment process by which pigment in dichromated gelatin is exposed to light through a negative. The areas that are exposed to light harden and the rest is washed away, leaving a photograph that has relief: areas of darker, thicker pigment and highlights that consist of an exposed primary support.

Chromo-crystal – An oval collodion positive, face mounted to a piece of ruby glass. These photographs do not measure above 1.5 inches in diameter.

Collodion wet plate - Several binder tones are possible, such as milky black, brown, gray, or yellowish, depending upon the developing process. Hand-coated plates will have irregular edges, thumbprints and other irregularities. See page --- in process history for clarification.

Crystoleum – a hand-tinted albumen or salted print, face mounted to convex glass.

Cutting ambrotype – a collodion positive, face-mounted to another sheet of glass with Canada Balsam.

Gelatin on glass - The edges of gelatin plates will usually be even, when compared with collodion plates. Typically, these plates will have a neutral image hue and will often have silver mirroring.

Hyalotype (Langenheim) – albumen positive on glass, used as a lantern slide or stereo plate. Will typically be backed with ground glass to diffuse the light as it passes through the plate.

Ivorytype – a hand-tinted albumen or salted print, face mounted to flat glass.

Joly plate – an additive color screen process with a grid work of red, blue and green lines.

Lippman plate – a gelatin silver color plate process, very rare.

Opaltype – a collodion, carbon or gelatin positive image on milk glass.

Orotone – a gelatin positive, backed with gold suspended in banana oil.

Relievo ambrotype – a collodion positive with a white or clear background. Sometimes the plate will be backed with a scene or colored paper.

Ruby-glass ambrotype – a collodion positive on colored glass.

Sphereotype – A variation of the ambrotype process where the plate is exposed through a tube so that there is no exposure around the perimeter of the sitter in an oval shape.

Vitrified photo on glass – this process will usually have slight relief between d-max and d-min areas. Surface will usually be glossy overall.

Woodburytype – Very similar in appearance to a carbon print. Woodburytype is a pigment process whereby pigment is deposited on glass with a metal press. The resulting print has relief, like a Carbon print.

Part 2. Deterioration and Conservation of glass supported photographs

Glass deterioration

Glass deterioration can be divided into two categories: chemical and physical. Chemical deterioration will manifest because of adverse environmental conditions. Physical deterioration is usually the result of improper handling and housing.

Chemical deterioration

“Sick glass” has always been a problem for conservators. There are several contributing factors affecting decay, the major ones being those of glass composition, poor founding practice and environment. Others are exposure to aggressive solutions, time and temperature. The usual symptoms are weeping and the formation of crystals. Weeping is often caused by the excess of alkali and the lack of sufficient lime and/or other stabilizing material in the batch. In general, glass with a high proportion of silica to modifiers will tend to be stable whereas if the proportion of modifiers is high then the glass will be much more readily attacked. UV light is known to increase surface corrosion and the presence of sulfur in the atmosphere is known to increase weathering problems.

The chemical nature of decay is varied and very complex. Some of it, such as the weeping and crizzling caused by an excess of alkali and a lack of stabilizers in the glass, is fairly simple but the results of attack by water can be much more complicated. Water is a primary agent of the environment that causes the deterioration of glass. The surface of a glass tends to react with water or even with a humid atmosphere and starts a continuing process in which the effect progresses further into the glass.

Poor storage in the very damp conditions that often prevail in cellars or attics can be a considerable contributory factor to this form of decay. There can be no doubt that poorly formulated glass, which has not been well stabilized or has been made with high alkali content in order to achieve low founding temperatures makes the surface vulnerable to attack.[67]

Figure 1 is an example of a poorly housed gelatin glass plate negative and the resulting glass decay that resulted (case study 7). The plate has been broken at some point and stabilized by applying tape to the upper left and bottom central edges, on the emulsion side, and sandwiching the plate between two sheets of modern glass. As the tape aged, the adhesive cross-linked and lost its tack, resulting in the loss of four shards in the top left corner of the plate (only two shards are still present). Black masking and electrical tape were then used in the center of each edge to hold the package together. This allowed the ingress of moisture as the environmental conditions fluctuated, resulting in the formation of droplets of alkali material that crystallized (Figure 2). When the sandwich was taken apart, it was discovered that the decay was present only on the sandwiching pieces of glass and not the glass plate negative. This would suggest that the sandwiching glass was of inferior quality and therefore more prone to decay than the negative plate, which was made of superior glass. More information on this treatment can be seen in Case Study #7.

Physical deterioration

Broken glass

An impact break is one that is caused by a crushing blow to the material (Figure 3). Glass is characterized as a brittle material and therefore, subject to brittle fractures with rapid crack propagation without significant plastic deformation. This variety of fracture may have a bright, granular appearance. They are characterized by an impact cone, where the most damage has been done, surrounded by radiating arcs. Glass is considered an amorphous solid, meaning that it lacks a crystalline structure and a fracture will not follow any natural planes of separation, consequently, glass can break in a conchoidal fracture: Cracks will run perpendicular to an applied stress: that is, the shard of a broken sheet of glass will have smooth fracture surfaces.

Blind cracks - Or are there breaks that do not carry through the whole shard. These have to be stabilized primarily to avoid further damage to the support.

Knowledge of stress states and how they affect glass is needed. Sheer stress that is parallel to a face of the material, normal stress that is perpendicular to the face of the material, tensile stress induced by pulling forces, or even compressive stress that can rupture the material are all potentially very harmful to glass with blind cracks and breaks that have not broken the image binder. If the break has not torn or damaged the image binder, these shards will need special attention and stabilization to prevent further damage. (Figure 4)

Transgrainular fractures are fractures that travel through the plain of the material, following the path of least resistance (Figure 5). These fractures are the cleanest and easiest to mend.

Case Studies

Introduction with index table

The following case studies are based on what I have encountered under the scope of my time at the George Eastman House conservation lab. The treatment of the interpositive of Abraham Lincoln allowed for many innovations regarding the repair of photographs on glass and that is the treatment on which the rest of the case studies are based. The following table is a guide to the case studies, with the objects listed along the top and the treatments in alphabetical order down the left column.

Case study #1: Conservation of the Abraham Lincoln Interpositive

Case study #2: Broken 8 x 10” glass plate negative

Case study #3: Impact shattered 4 x 5” glass plate negative

Case study #4: Broken 5 x 7” glass plate negative with losses

Case study #5: Broken ambrotype with image losses

Case study #6: Broken 1/16th plate ruby ambrotype with losses

Case study #7: 1/2 plate, passé-partout style ambrotype with backing losses

Case study #8: Broken 8 x 10” glass plate negative with deteriorated glass and losses

Case study #9: Opaltype with severely flaking emulsion

Case study #10: Broken stereo plate on bent glass

Case study #11: Lantern slide with a broken cover glass

Preventive Measures


The most common cause of breakage in the lab is the object slipping out of the conservator’s hands when wearing cotton gloves. Neoprene or Latex gloves should be used instead to protect the emulsion from fingerprints that will cause deterioration over time.

  • Glass fragments should be handled as little as possible. To that end, virtual

assembly in PhotoShop may be necessary to determine the arrangement of the shards. See Appendix 3.

  • A padded (foamed polyethylene) and tight weave tissue or Sintered Teflon

lined box should be used for fragments. Do not let the fragments come into contact with the foam; any lifting binder will be very susceptible to snagging.

  • Handle glass plates by two edges and carry flat. Do not handle by the


  • Work on a clean, dry, padded surface: such as a sheet of thin Ethafoam covered

with blotter.

  • Place glass plates on a flat surface binder side up.
  • Never place any pressure on plate: label sleeves before placing the plates in


  • Never stack bare plates.
  • High use plates should be duplicated.
  • Do force the hinges closed on cased images.
  • Do not disassemble cased image without a photograph conservator.

Housing Recommendations

Intact bare plates with no flaking

House glass plates in four-flap enclosures and envelopes. All materials should pass the P.A.T. The four-flap enclosure will insure that any incipient flaking will not be exacerbated by inserting and removing the plate while sliding it out of the envelope. If four-flap enclosures are not feasible, the plates should be placed in the envelope binder side away from the seam to ensure there is no abrasion of the binder and that the adhesive cannot cause deterioration. This enables the object to be put into and removed from the enclosure without the risk of scratching that can result from sliding the object into and out of an envelope.

Plates should be stored vertically in document boxes, on the long edge. Interleave every inch with acid-free cardboard to support the plates[68]. The plates should be housed vertically, on their long edges, in a partly filled box with a spacer to minimize jostling during handling. For plates over 10 x 12”, use over sized legal boxes. Only partially fill the box to prevent the box from becoming too heavy[69]. Acid-free corrugated board should be used to fill out the box to avoid shifting of the contents.

Boxes of glass plates should be stored on lower shelving and never above about four feet to prevent someone from having the lift the plate down from above their head. The boxes should further be labeled clearly: FRAGILE, HEAVY, and GLASS.

Intact bare plates with flaking binder

If the flaking is minor, i.e. a few small edge losses with no flaps or flaking towards the center of the plate, the plates should be housed in four-flap enclosures within their envelope. The envelope should be labeled: FLAKING EDGES, remove with care.

More severely flaking plates, i.e. plates with hanging flaps and/or cracking overall with incipient flaking in the center, should be duplicated and housed in fourflap enclosures within their envelope. Plates with more extensive flaking should be stored in sink-mats and stored horizontally. Housings should be labeled accordingly.

Broken plates

Broken plates deserve special attention. It is very important that broken shards do not come into contact with each other. This can cause damage to the binder and the glass edges such as chipping and additional breakage. Create a form-fit support by cutting 3 pieces of 4-ply mat board and place one on the shards on one of the pieces of mat board, emulsion side up, and trace the edges of the shard. Remove the shard and cut out the form, leaving two 2 pieces that will fit to the shards. Attach one of these pieces to a full size board and the second form to the second piece of board (Figure 61[70]) with wheat starch paste or 3M #415 double-stick tape. The shards should sit level to below the top surface of the mat. The objective is to support each piece so that additional damage will not occur by placing the shards in contact. These are then placed in separate 4-flap enclosures and housed flat, and marked “broken plates / carry flat”.

An alternative housing for plates that have been broken into many shards is suggested in a 1991 paper[71] by Constance McCabe of the National Archives in Washington D.C.:

“Broken negatives are assembled in proper orientation for duplication but are housed in sink mats with the components separated with paperboard spacers attached with adhesives to avoid mechanical damage to the glass pieces… [Paper tabs are inserted] to assist in lifting out large pieces. These enclosures muse be carried horizontally or the glass will slip away from its support… Negatives housed in sink mats are stored horizontally in stacks of three to six (depending on the size and weight) within storage boxes. Boxes are of the dropfront style with metal stays… Each box is marked with the cautionary label: “Caution: Broken glass. Carry Horizontally”.”

It is extremely important that broken negatives housed in a sink-mat include pieces of paperboard to separate the shards. If this is not done, the shards will rub together, causing flaking of the binder and grinding of the glass. The sink mat should be constructed of mat-board and care should be taken that if there is any flaking binder that it is not exacerbated by rubbing on the edge of the sink-mat. A sintered Teflon lining will minimize this possibility.

Cased images should be hosed in four-flap enclosures with a thumbnail photograph of the object on the outside of the box so that it can be determined what is in the box without opening the enclosure. Objects should be stored flat in larger boxes or padded drawers, or vertically in padded slots in boxes or drawers. Do not house glass plates in plastic sleeves.


Control of Relative humidity offers a significant improvement in the long-term preservation of photographic materials. A slight increase in RH will lead to the deterioration of the silver, binder, varnish and glass support, and a slight decrease on RH can lead to flaking of binder, and dehydration of the glass. Connie McCabe[72] recommends 30-40% RH. Below 30 and the binder will desiccate and above 40 the glass will start hydrating.

Stephen Koob of the Corning Museum of Glass recommends that the following guidelines be followed:

  • No fluctuations in conditions
  • Avoid temperature extremes
  • Avoid spot-lighting (leads to uneven heating)
  • Avoid cycling.

Cased images have their own requirements when it comes to their preservation. The base recommendations are 18 – 20°C and 40-50% RH. Do not store cased images <40% RH to prevent embrittlement of the case, and do not store them >50% RH to prevent brass mat and cover glass deterioration.

For all photographs on glass, the light levels should be kept below 50 lux (5 footcandles) when they are on display.


Glass and photography go hand in hand. From cameras lenses, to glass plates, to enlargers and even frames, glass is has been integral to the art and science of photography since its inception. There are more than 20 photographic processes on glass, and when the permutations and variations of these are taken into consideration, the number increases to no fewer than 40 processes. In order to treat photographs properly, one must understand their history and production.

The treatment of the Abraham Lincoln interpositive presented the perfect opportunity to examine innovative treatment options for broken photographs on glass. As a result, many groundbreaking treatment options have been explored. Some other treatment options have been explored in the course of this research in the series of case studies.

This research has been an initiative to expand research into the history, care and treatment of this valuable part of the history of photography. This report has only touched how to fully understand the conservation of glass supported photographs. It is hoped that this report will encourage further research.

Appendix 1: The history of glass as a support for photographs

Appendix 2: Historic treatments

Appendix 3: Virtual assembly of a broken photograph with PhotoShop

Appendix 4: Double-view housing instructions


This project would not have been possible without the support of many people.

I would like to thank the Andrew W. Mellon foundation and Angelica Rudenstine for generously funding the Advanced Residency Program for 5 cycles. I would also like to thank the co-directors of the program, Grant Romer and Jim Reilly whose tireless work has made it possible for the program to function. I would especially like to thank Grant for his inspiring conversations. He is always willing to take the time to speak with any fellow seeking advice.

I would also like to thank my advisers: process historian Mark Osterman for sharing his vast knowledge of the photographic processes and techniques of the 19th century. His input has been invaluable in the writing of this project. Jiuan-Jiuan Chen, my advisor regarding the conservation area of this project, kept me on track when I wanted to veer off and take on too much. Her support in organizing this project was extremely valuable.

Thank you to the staff and fellows of the ARP as well, especially Stacey VanDenburgh for her humor, excellent record keeping and candor. I would especially like to thank fellows Luisa Casella and Karina Kashina (now Beeman), their friendship was always encouraging and much needed as I was in the throes of writing up this research. Gawain Weaver was also very helpful in my section on colour processes; his generosity in providing the microscopic photographs saved me a lot of work.

I would like to thank the staff of the George Eastman House, especially David Wooters and Joe Struble for granting me access to the Langenheim and Niepce plates. Being able to see them was one of the highlights of conducting my research in the archives. Joe was especially generous and patient in letting me explore the many glass supported photographic process examples in the collection. In addition, I would like to thank Barbara Galasso for the many photographs she provided to me for this project.

Many individuals have shown interest and helped my throughout this research. I would like to thank them, in no particular order: Mark Harnley of the Getty Museum for his interest and advice regarding my project. Christa Hoffman of the Austrian National Library, for speaking with me about her interests regarding the deterioration of photographs on glass. John McElhone for his interest and encouragement and finally, Martin Scott for his friendship, generosity and advice regarding the dynamics of conserving glass supported photographs.

I would also like to thank the people who assisted me in my research in Europe: Ann Deckers and Pool Andres of the Belgium National museum of photography for the invaluable information they provided regarding glass production in Belgium. Colin Harding of the National Media Museum in Bradford, England for spending the day with me, exploring the work of Thomas Skaife and his Pistolgraph. Michael Pritchard of Christie’s London for meeting with me to discuss my research and Thomas Skaife. And finally, Peter Hingley of the Royal Astronomical Society for generously providing me with a wealth of information regarding Sir William Herschel and his contemporaries. His enthusiasm and humor made my visit most enjoyable.

Finally, I would like to thank Dan Trommater for his undying support, humor and enthusiasm throughout this process of uprooting himself once again and coming to Rochester with me, Maryann Whitman for her patience with my many drafts and superb editing, and finally Doug Whitman for his unique humor and outlook on life.

  1. The British Journal of Photography 1864, p.491.
  2. (http://www.nicephore-niepce.com/pagus/invus5.html)
  3. The Photographic News, June 21, 1872, 293
  4. Philosophical Transactions of the Royal Society, 1840: 12; and Herschel, A.S. “On some original glass photographs produced and preserved by the late Sir John Herschel, Bert., from his earliest Experiments on the Chemical Properties of Light.” The Photographic Journal, June 15, 1872: 153.
  5. Herschel’s experimental notes, 1839.
  6. Herschel, A.S.: 154
  7. Letter, Talbot to Herschel, 29 March 1843.
  8. See also Robert Hunt’s Manual of Photography
  9. Eder 340.
  10. Mark Osterman, correspondence
  11. Anthony’s Photographic Bulletin, Vol.19, 1888:558; Photographic Arts Journal, Vol. 6, 1853:148
  12. Photographic Art Journal Vol.16, 1853: 148-149
  13. Werge, The Evolution of Photography: 52-53.
  14. Anthony’s Photographic Bulletin Vol. 16, 1885: 247-249
  15. Mark Osterman, communication
  16. Eder 339.
  17. http://www.daguerreotype.com/l_table.htm#Langenheim,%20Frederick
  18. Spindler 1-15.
  19. Browne 222
  20. Ibid. 1-15.
  21. Gernsheim 195
  22. Patents for Inventions 55-56
  23. Ibid. 113-114
  24. Ibid. 88
  25. Jones 90
  26. Patents for inventions v.1, 88-89
  27. Wilson 100
  28. Patents for Inventions 97, 148. There were many patents taken out by Woodbury in the intervening years, improving upon the Woodburytype process: No.105, 1866, No.1315, 1866, No.1918, 1866, No.346, 1870, No. 2171, 1870, No. 3654, 1872 and No.1954, 1873
  29. Patents for inventions v.2, 21-22
  30. Cassell’s 565
  31. The collotype process was an early printing process. A glass plate was coated with sensitized gelatin and exposed under a negative. Light passed through the negative would harden the gelatin on the glass plate. The unexposed gelatin would then be washed away with water, leaving the hardened, exposed gelatin. The washed glass plate would be coated with ink, adhering to the exposed gelatin and printed onto fine paper.
  32. The British Journal of Photography (26 Feb. 1875), 103
  33. Photographic Journal, 7 (15 Feb., 1861), 99–101
  34. The Times,, 10th September 1852
  35. Gernsheim 119
  36. Patents for Inventions v.1, 34-35
  37. Collodion Journal 5:19, 2
  38. Gernsheim 237
  39. Bisbee, US patent No. 14,946
  40. Mettam, R. 1
  41. Skaife, Brighton Herald, 8
  42. Skaife, 1860. 36.
  43. Letters to a photographic friend 1860, 241.
  44. Skaife, 1861 advertisement in the London Times
  45. Patents for inventions v.1, 82.
  46. Egunnike 13
  47. The British Journal of Photography,1864
  48. Egunnike, 1
  49. Patents for Inventions, Vol. 1, 108-109.
  50. The Liverpool and Manchester photographic Journal, 1857, p.232
  51. Ibid. p.231
  52. The Photographic Journal, 15 March 1862, 101
  53. Patents for Inventions v.1, 2
  54. The British Journal of Photography, March 15, 1862, 102
  55. Journal of the Photographic Society 1859, 153
  56. Ellis 34.
  57. Woodbury 331
  58. Monckhoven 478
  59. Eder 373
  60. Patents for Inventions, v.1, 67.
  61. Towler 245.
  62. Eder
  63. In 1901 Maddox received the Royal Photographic Society's Progress Medal for inventions that led to the foundation of the dry plate and film industry.
  64. http://en.wikipedia.org/wiki/Edward_S._Curtis
  65. Davis, 68
  66. A term coined by Mark Osterman.
  67. Bray 93.
  68. www.archives.gov/preservation/storage/glass-plate-negatives.html
  69. ibid
  70. Herskovitz 4.
  71. Preservation of 19th-Centure Negatives in the National Archives 1991, 68-69.
  72. McCabe, 1991; 40

Katharine Whitman, was an ARP fellow from 2005 to 2007. In her capstone project, Kate looks at a little understood photographic support materials, glass. Currently Kate is the Conservator of Photographs at the Art Gallery of Ontario in Toronto, Canada.