Identification

Collodion POPs

common use: 1885-1910

Format

The majority of collodion POPs were produced as cabinet cards, a 4.25" x 6.5" paperboard mount format. The process was used extensively for commercial portraiture in the 1890s.

Image Tone

Collodion POPs have characteristic reddish-brown to purple image tones, a product of the gold toning that was necessary for the stability of the prints.

Iridescence

The greatest problem with identifying collodion POPs is distinguishing them from gelatin POPs. One of the most accurate ways to identify the process is to look for iridescence, a propery caused by the collodion emulsion. To do this simply move the print around while observing the reflectance of a light source off the print’s surface; a fluorescent light works best. While not all collodion POPs exhibit iridescence, many do, and the technique is by far the simplest non-destructive means of identification.

Layer Structure

Collodion POPs have a baryta layer between the emulsion and the paper support that acts to obscure paper fibers. Under relatively low magnification one can inspect the surface of a print for an absence of visible paper fibers.

Abrasion

Collodion emulsions are particularly susceptible to abrasion; even light scratches will often appear white due to the removal of image.