Instructions: A Visual Glossary of Six Stages of Acetate Film Base Deterioration

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Cellulose acetate is difficult to distinguish from other film bases. Methods of identification include: edge printed with “SAFETY,”Footnote 1 various notch codes in upper right corner (emulsion facing up), dating information, polarization (see POLARIZATION VIEWER), or destructive testing such as the diphenylamine test, the burn test and the float test).

Edges of several negatives


  • Deterioration of cellulose acetate can be categorized into six stages.
  • In general until stage three deterioration, negatives will have legible photographic detail and can still be duplicated.
  • Image legibility is decreased in the final fourth, fifth and sixth stages. The negatives at these stages should be digitized before the image fades away and placed into cold storage before further deterioration occurs, or destroyed.
  • Deterioration may not be uniform across the image, so the stage of deterioration should be determined by assessing the worst area.

Stage 1

  • Legible image
  • No visible deterioration
  • Acid detecting strips called A-D StripsFootnote 2 can be used to measure deterioration
three negatives with no deterioration

Stage 2

  • Legible image
  • Odor of vinegar (acetic acid)Footnote 3 can be detected
  • Begins to curl
three slightly curled negatives

Stage 3

  • Legible image
  • Odor of vinegar (acetic acid) is present
  • Begins to shrink
  • Becomes brittle
three slightly curled and yellowed   negatives
  • Dyes in the anti-curl layer may turn pinkFootnote 4 or blueFootnote 5 due to a change in pH in the gelatin layer
several negatives with with blue and pink coloration on the edges

Stage 4

  • Legible image
  • Warping
  • Odor of vinegar (acetic acid) is present
two warped negatives

Stage 5

  • The image may or may not be legible
  • Odor of vinegar (acetic acid) is strong
  • Bubbles and crystalline deposits form between the layers of the negative
four negatives with bubbling

Stage 6

  • The image may or may not be legible
  • Gives off a very strong odor of vinegar (acetic acid)
  • Channels form on both the emulsion side and the film base side of the negative
four negatives with channels
eight negatives with channels


Bennett, Karen L. and Jessica S. Johnson. “Identification of Film-Base Photographic Media,” National Parks Service Conserve O Gram, No. 14/9, 1999.

Fischer, Monique. “A Short Guide to Film-Based Photographic Materials: Identification, Care and Duplication,” NEDCC Technical Leaflet, updated 7/2012.

Reilly, James. IPI Storage Guide for Acetate Film, Rochester, New York: Image Permanence Institute, Rochester Institute of Technology, 1993.

Valverde, María Fernanda. Photographic Negatives: Nature and Evolution of Processes, Rochester, New York: Advanced Residency Program in Photograph Conservation, 2005.


Tania Passafiume
Head Conservator of Photographic Materials

Emma Hamilton-Hobbs

Eli Eaton

Tom Thompson
Multimedia Production Specialist

Anna Lehn
English Editor

Special thanks to Janet Kepkiewicz

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