Exploring

Inherent Vice: Film Supports

Structural Layers

While degradation of the substrate is usually the primary cause of damage to film-based collections, the binders and image forming materials are also subject to deterioration.

Binders/Emulsion

The gelatin binder on this glass plate negative has dissolved as a result of exposure to water.

Collodion was used as a binder for collodion glass plate negatives and lantern slides. Gelatin was introduced about 20 years later and used for gelatin dry plate negatives and transparencies such as lantern slides and autochromes (an early color process).

Lantern slides first used an albumen binder and later wet collodion and dry gelatin binders. Since lantern slides and autochromes had a glass covering that was taped around the edges, their emulsions are somewhat more protected. However, broken tape seals and cracked or broken cover glass do occur and can allow moisture to enter and emulsions to crack and peel.

Collodion glass plate negatives sometimes had a subbing (a thin coating, usually albumen), which was applied to the glass plate to help the collodion adhere to the glass. In addition, a varnish coating was placed over the emulsion for protection, since it was very fragile and subject to abrasion. Gelatin dry plate negatives were also coated with a subbing, or they were chemically etched to help the emulsion adhere to the glass. Gelatin dry plates were usually not varnished. In general, gelatin binders are subject to softening and mold growth in high relative humidity, as well as flaking due to shrinkage of the gelatin in low relative humidity.

High humidity has caused the emulsion on this nitrate negative to become soft and sticky; parts of the enclosure remain adhered to the negative.

Nitrate, acetate, and polyester films all use gelatin as their binder material. Nitrate and acetate films also had a subbing of diluted cellulose nitrate to help the binder adhere to the film. In addition, nitrate (after 1903) and acetate had an anti-curl layer of gelatin applied to the back of the film. The tendency of gelatin to soften in high humidity is made worse by the byproducts of nitrate deterioration, which cause the emulsion to become very soft and sticky. In acetate and polyester films, the gelatin is vulnerable to softening and mold growth in high humidity, but is otherwise not a major contributor to deterioration.