Film

From Silvergrain Labs

Film is usually negative material to be exposed in camera. Photosensitive emulsion is coated on flexible film, such as oil-treated paper, cellulose nitrate, cellulose acetate (hydrated), cellulose triacetate, and polyesters, such as poly(ethylene telephthalate) or poly(ehylene naphthalate).

Modern Film Bases

• sheet films

most are coated on poly(ethylene telephthalate) films (usually called polyester or PET).

• roll films

most are coated on triacetate films.

• APS films

All APS films are coated on annealed poly(ethylene naphthalate) as this base has much better curling properties than the two above, and also has excellent dimensional stability.

In-Camera Material

Cellulose nitrate films are extremely inflamable (See: [1]) and they are also inferior in keeping properties. Nitrate film of important images are usually duplicated onto film and also by high resolution digital scan, and the original copy is stored in a closed container in freezer. Early cellulose acetate films are not flammable but their archival property is also inferior. Take dupes and digital scans, and then keep the original in at refrigeration temperature.

Cellulose triacetate films are better film material than nitrate and early acetate films. However, these films still undergo acid hydrolysis and therefore a close attention is required for storage conditions. These films enjoy the best longevity if stored in fresh, circulating air of low humidity. Closed container is harmful because of accumulation of the acid in the environment. High humidity is also detrimental because humidity accelerates the acid hydrolysis of the triacetate. There are some modern improvements where the hydrolysis is slowed down by chemical additives in the film base, but the exact nature of this is unknown.

Modern sheet films are coated on poly(ethylene telephthalate) or PET film base. This is often called polyester base, since PET is a polyester. This type of film base has severe curling property and not very suitable for roll film applications, but it has excellent dimensional stability and is very suitable for sheet films. The material is highly archival, and the film base itself is not affected by humidity. (However, the image silver is still affected by humidity.)

With the APS (Advanced Photo System), the film base plastic also saw advancement. The plastic base used for APS films is annealed poly (ethylene naphthalate) and this material is equipped with the best of triacetate films (lower curling property) and PET (excellent archival property and dimensional stability). However, even in 2006, we don't see this plastic film used in 35mm or mediun format films sold by Kodak or Fujifilm.