Putting It Into Practice

Evaluating Your Collections

Microforms

Many cultural collections include older microfilms or microfiche, which may have been produced as a preservation copy of paper-based collections or may have been surrogates for original materials that were discarded, such as newspapers. These microforms may be positives or negatives, either master or duplicate. Many of them will be silver-gelatin microfilm, but diazo microfilm (which uses dyes) and vesicular microfilm (in which an image is formed by heating the film to form bubbles) may also be present. Diazo microfilm will fade on exposure to light, and vesicular microfilm is very vulnerable to heat damage. Microfilm has been produced on nitrate, acetate, and polyester film through the years, so older microfilm must be inspected to determine its type.

As the acetate base of this microfilm broke down, it shrank, the emulsion warped and became sticky, and the film adhered to itself. Unwinding the film caused it to tear.

Chemical damage may include evidence of nitrate or acetate deterioration. Evidence of chemical damage due to the deterioration of nitrate film may include yellowing, stickiness, and a nitric acid odor. Nitrate films that are in an advanced state of deterioration will be soft and may adhere to adjacent films or enclosures, or they may have partially disintegrated into a brown powder. Evidence of chemical deterioration of acetate film due to vinegar syndrome may include a vinegar odor, curling or staining. Advanced deterioration will manifest itself through bubbles on the film and separation of the emulsion from the base. Nitrate or acetate film may sometimes be identified by edge printing (it will say NITRATE or SAFETY).

Silver gelatin microfilms are subject to oxidation, which can result in small blemishes (called measles). This phenomenon is made worse by high humidity and the presence of pollutants. Diazo microfilms may exhibit fading, and vesicular microfilms may exhibit image loss from heat damage.