Collodion is guncotton (cellulose nitrate) in a solvent. It was used for
stripping because it had poor adhesion to glass - it was used in the
wetplate process. Photogs of the period had all kinds of formulas to make
the darn stuff stick well on glass, including a substrate of gelatin, but
also many other exotic materials. But collodion is definitely NOT gelatin,
nor can the two be substituted for each other. And I certainly wouldn't want
to fool around with guncotton! (Just think of early photogs - using mercury,
vaporized iodine, guncotton - the EPA would drive them all out of business.)
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@iag.net