A malleable pinkish metal used in the daguerreotype process.
Thin copper plates were coated with pure silver by either electroplating
or applying a separate plate of silver on the copper
and compressing the two plates between steel rollers.
↑Osterman, Mark. 2007. Copper, Cu. In The Focal Encyclopedia of Photography: Digital Imaging, Theory and Applications, History, and Science, ed. Michael R. Peres, 65, Focal Press.