The effect of the emulsion

Because film without emulsion breaks down more rapidly, another question arises: what part is played by the emulsion itself - by the presence of gelatine? It seems that the gelatine is actually acting to stabilize the material, probably mainly because gelatine is itself a polymer system made up of amino acids and linked into long chains, into a protein-type material. When the degradation products (the acetic acid) from the base hit the emulsion, the emulsion serves as a mop for the acid. When it takes up the acid, the emulsion itself is broken up and is lost: you can then wipe off the silver image and the emulsion becomes sticky. Because film is wound tightly into a reel and is, therefore, a sandwich of support material and emulsion, we believe that the emulsion also somehow acts as a diffusion barrier to, perhaps, the ingress of oxygen.

Also, negative film has a thicker layer of emulsion than positive film, so we took a cross section of degraded stocks in an archive and compared percentage incidences of positive and negative films exhibiting vinegar syndrome. We found that positive films formed around 59% of degraded material compared to negative films only 41%. The emulsion layer itself is beneficial.