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Table 1 Characteristic physical and visual signs of cellulose nitrate and cellulose acetate deterioration [6, 25]

From: Rapid identification of cellulose nitrate and cellulose acetate film in historic photograph collections

Level Cellulose nitrate Cellulose acetate
1 No visible deterioration No visible deterioration
2 Film base turns yellow, and image shows signs of mirroring Film base begins to curl and can turn red or blue
3 Film base becomes sticky and gives off a strong smell of nitric acid Film base shrinks, becomes brittle and produces acetic acid (vinegar smell)
4 Film base becomes amber in colour and the image begins to fade Film base can begin warping
5 Film softens and can weld to adjacent material or enclosure Film base forms bubbles and crystals
6 Film turns into a brown acid powder Film base forms channels