Each color is separated by a gelatin layer that prevents silver development in one record from causing unwanted dye formation in another.
The gelatin layer is then pressed onto a paper support.
This is caused by antihalation dyes, which are normally colorless and incorporated into the gelatin layer.
The film may be soaked in water to swell the gelatin layer.
The spot will darken as dye accumulates in the gelatin layer.
These can be removed by careful knifing of the gelatin layer.
Most fiber-based papers include a clear hardened gelatin layer above the emulsion which protects it from physical damage, especially during processing.
"Once you've got a serious crack through the gelatin layer, it often doesn't go back."
The prints are made on paper with a thick gelatin layer that has been sensitized with dichromate salts.
The irregular thickness of the gelatin layer can, in unfavourable conditions, lead to stresses in the pictorial layer, which can be damaged this way.