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Table 2 Traditional methods used by cultural heritage institutions for identification of photographic plastic film bases

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

  Cellulose nitrate Cellulose acetate Polyester Evaluation of technique
Contextual information   Non-invasive
No WHS Concerns
Not always available
 Date [6] ? ? ? Requires verification: periods of use overlap.
Visual examination   Non-invasive
No WHS Concerns
Physical characteristics not always present
 Edge printing [6]
Nitrate’

Safety’

‘Estar’
‘Cronar’
Requires verification: film duplication (for example from nitrate to polyester) can include previous edge printing
 Notches [47] x
Usually ‘V’
x
Usually ‘U’
? Requires verification: different manufacturers used notches to mean different things
 Deterioration [48] ? ? x Requires verification: some deterioration is common to both
 Polarisation test [48] x x
Shows interference colours
Only identifies polyester
Requires verification: does not distinguish between cellulose nitrate and cellulose acetate
Chemical testing   Invasive & destructive (requires sample)
WHS concerns (solvents or by products)
 Float test [48] Requires verification: results can be difficult to interpret, since there are many different types of cellulose nitrate and acetate manufactured, and deteriorated film behaves diversely
 Diphenylamine spot test [49] x x Requires verification: cellulose acetate and polyester sometimes have a subbing layer of cellulose nitrate —can create a false positive.
 Burn test [48] x x Requires safety measures: must be performed outdoors, requires bucket of water, and is generally no longer conducted