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

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return to "The History and Conservation of Glass Supported and Protected Photographs"
return to Research from the Andrew W. Mellon Advanced Residency Program in Photograph Conservation at George Eastman House 1999-2009


Treatment Synopsis

The ambrotype was removed from the frame and opened from the back of the passépartout. The housing was cleaned and a new backing of acrylic velvet paper was placed behind the image plate.


Previous Treatment: The original backing of the passé partout (European) has been replaced with a brown paper and the entire package has been placed in a later period, Ogee style (American) frame.


Passé-partout: The original binding tape is present and torn at the corners and along the edges. The cover glass is in fair condition with some mild deterioration on the inner surface and soiling on the outer surface. The window mat is in very good condition

Frame: The backing board is warped, stained and held in with two modern nails. The plate housing is shored into the frame with two ball-point pens.

Image Plate: Upon initial examination, the binder and image are in very good condition. The black backing material is flaking with some losses. The image plate was coated with asphalt on the emulsion side.


  • The passé-partout housing was opened from the recto mechanically with a dull scalpel.
  • Upon opening the passé-partout it was determined that the housing was in good condition and only cleaning was needed. The glass was cleaned with 50:50 alcohol/distilled water, swabbed on.
  • The glass side was cleaned with 50:50 alcohol/distilled water, swabbed on.
  • The plate was replaced in the passé-partout and held in place with P-90 Filmoplast tape, and backed with a piece of black acrylic velvet. The paper backing was then replaced, using PVA.
  • The paper tape edges of the passé-partout were consolidated with PVA and fills were done with Golden acrylic toned Japanese tissue.
  • Additional in-painting was done with Winsor and Newton watercolours.


This was a rather simple and highly successful treatment. The visual continuity of the image plate was renewed with minimal impact on the original object materials.

Notes on reticulating black varnish

Reticulating varnish has traditionally thought to be the result of poorly formulated varnish. However, there is evidence that some reticulation may be caused by glass deterioration beneath the varnish[1]. Varnish can undergo some plastic deformation, causing air pockets between the glass and varnish that appear as distracting lighter areas when the plate is viewed. In other cases, the varnish may crack first, allowing the ingress of moisture and resulting in hydrolytic glass deterioration, compounding the problem.

Various modern varnishes have been recommended for the replacement of reticulating historic varnishes. However, glass deterioration will affect the new varnish with any fluctuations in relative humidity. Stabilization at the proper relative humidity will mitigate additional corrosion.

The introduction of a separate black backing, such as acrylic (non-hygroscopic) black velvet, will restore the aesthetics of the plate without disturbing the historic varnish. Additionally, the introduction of B-72 into the air pockets is another option to stabilize the reticulating varnish. However, this non-reversible treatment can be very delicate and time consuming.

Chemical analysis[2], conducted by Susie Clark in 1998, of black varnish has shown the layers to consist of shellac, soot and lamp black. The research goes on to suggest either the use of modern materials such as a mixture of carbon black and B-72 in acetone or a traditional mixture of shellac in methylated spirits and carbon black for the in-painting of lost black varnish. While these are viable options, these alternatives obliterate the original backing.

  1. Clark 231
  2. Ibid 235

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.