Film stock

It is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals.

[1] The emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use.

Instead, a very short exposure to the image formed by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal.

Dyes, which adsorb to the surface of the silver salts, make the crystals sensitive to different colors.

Early motion picture experiments in the 1880s were performed using a fragile paper roll film, with which it was difficult to view a single, continuously moving image without a complex apparatus.

The first transparent and flexible film base material was celluloid, which was discovered and refined for photographic use by John Carbutt, Hannibal Goodwin, and George Eastman.

Eastman Kodak made celluloid film commercially available in 1889; Thomas Henry Blair, in 1891, was his first competitor.

[citation needed] Blair's new company supplied European filmmaking pioneers, including Birt Acres, Robert Paul, George Albert Smith, Charles Urban, and the Lumière Brothers.

By 1896, the new movie projector required a fully transparent film base that Blair's American operation could not supply.

If longer lengths were needed, the unexposed negative rolls could be cemented in a darkroom, but this was largely undesirable by most narrative filmmakers.

The makers of Actuality films were much more eager to undertake this method, however, in order to depict longer actions.

Eastman increased the length of rolls to 200 feet without major adjustments to the emulsion, retaining a large market share.

Lumière reformulated its stock to match the speed of Eastman film, naming it 'Etiquette Violette' (Violet Label).

A significant number of fatal accidents occurred in theatrical projection booths, where the heat of the projector lamp made ignition a possibility.

In 1909, tests showed cellulose diacetate to be a viable replacement base, and Kodak began selling acetate-base films the following year in 22 mm widths for Edison's work on the Home Kinetoscope, which was commercially released in 1912.

[6] The stock's increased sensitivity to red light made it an attractive option for day for night shooting.

Panchromatic film stock increased costs and no motion pictures were produced on it in their entirety for several years.

Orthochromatic film remained dominant until the mid-1920s due to Kodak's lack of competition in the panchromatic market.

Technicolor introduced a color reversal stock, called Monopack, for location shooting in 1941; it was ultimately a 35 mm version of Kodachrome that could be used in standard motion picture cameras.

Kodak discontinued the manufacture of nitrate base in 1951, and the industry transitioned entirely to safety film in 1951 in the United States and by 1955 internationally.

The emulsion consists of silver halide grains suspended in a gelatin colloid; in the case of color film, there are three layers of silver halide, which are mixed with color couplers and interlayers that filter specific light spectra.

Different emulsions and development processes exist for a variety of image recording possibilities: the two most common of which are black and white, and color.

The film is also distinguished by how it is wound with regard to perforations and base or emulsion side, as well as whether it is packaged around a core, a daylight spool, or within a cartridge.

Speed determines the range of lighting conditions under which the film can be shot, and is related to granularity and contrast, which influence the look of the image.

The stock manufacturer will usually give an exposure index (EI) number equal to the ASA which they recommend exposing for.

However, factors such as forced or non-standard development (such as bleach bypass or cross processing), compensation for filters or shutter angle, as well as intended under- and over-exposure may cause the cinematographer to actually "rate" the stock differently from the EI.

While black-and-white film has no color temperature itself, the silver halide grains themselves tend to be slightly more responsive to blue light, and therefore will have daylight and tungsten speeds — e.g. Kodak's Double-X stock is rated 250D/200T, since the tungsten light will give slightly less exposure than an equivalent amount of daylight.

All plastic is subject to deterioration through physical or chemical means, and thus, motion picture film is at risk for the same reason.

Cellulose nitrate, because of its unstable chemistry, eventually breaks down, releasing nitric acid, further catalyzing the decomposition.

Modern polyester-based stocks are far more stable by comparison and are rated to last hundreds of years if stored properly.