Film stock

Film stock is an analog medium that is used for recording motion pictures or animation. It is recorded on by a movie camera, developed, edited, and projected onto a screen using a movie projector. 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. The sizes and other characteristics of the crystals determine the sensitivity, contrast and resolution of the film. 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. This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph. In addition to visible light, all films are sensitive to X-rays and high-energy particles. Most are at least slightly sensitive to invisible ultraviolet (UV) light. Some special-purpose films are sensitive into the infrared (IR) region of the spectrum.

In black-and-white photographic film there is usually one layer of silver salts. When the exposed grains are developed, the silver salts are converted to metallic silver, which blocks light and appears as the black part of the film negative. Color film has at least three sensitive layers. Dyes, which adsorb to the surface of the silver salts, make the crystals sensitive to different colors. Typically the blue-sensitive layer is on top, followed by the green and red layers. During development, the exposed silver salts are converted to metallic silver, just as with black-and-white film. But in a color film, the by-products of the development reaction simultaneously combine with chemicals known as color couplers that are included either in the film itself or in the developer solution to form colored dyes. Because the by-products are created in direct proportion to the amount of exposure and development, the dye clouds formed are also in proportion to the exposure and development. Following development, the silver is converted back to silver salts in the bleach step. It is removed from the film in the fix step and is sometimes recovered for subsequent use or sale. Fixing leaves behind only the formed color dyes, which combine to make up the colored visible image. Later color films, like Kodacolor II, have as many as 12 emulsion layers, with upwards of 20 different chemicals in each layer. Photographic film and film stock tend to be similar in composition and speed, but often not in other parameters such as frame size and length.

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. The stock had a frosted base to facilitate easier viewing by transmitted light. Emulsions were orthochromatic. By November 1891 William Dickson, at Edison's laboratory, was using Blair's stock for Kinetoscope experiments. Blair's company supplied film to Edison for five years. Between 1892 and 1893, Eastman experienced problems with production. Because of patent lawsuits in 1893, Blair left his American company and established another in Britain. Eastman became Edison's supplier of film.^{[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. Eastman shortly thereafter bought the company out and became the leading supplier of film stock. Louis Lumière worked with Victor Planchon to adapt the Lumière "Blue Label" (Etiquette Bleue) photographic plate emulsion for use on celluloid roll film, which began in early 1896.^{[citation needed]}

Eastman's first motion picture film stock was offered in 1889. At first the film was the same as photographic film. By 1916, separate "Cine Type" films were offered. From 1895, Eastman supplied their motion picture roll film in rolls of 65 feet, while Blair's rolls were 75 feet. 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. They created cemented rolls as long as 1,000 feet. American Mutoscope and Biograph was the first known company to use such film for the Jeffries-Sharkey fight on 3 November 1899.

As the quantity of film and filmmakers grew, the demand for standardization increased. Between 1900 and 1910, film formats gradually became standardized and film stocks improved. A number of film gauges were made. 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). Blair sold his English company to Pathé in 1907 and retired to the US. Pathé began to supplement its operation in 1910 by purchasing film prints, stripping the emulsion from the film base and re-coating it. 35mm film began to become the dominant gauge because of the commonality of Edison's and Lumière's cameras. Consumers usually purchased unperforated film and had to punch it by perforators that were often imprecise, causing difficulty in making prints for the opposite perforation format. In 1908, the perforators began to be made by Bell and Howell. Eastman Kodak used the Bell and Howell machine to perforate its films. In 1909, Edison's organization of the Motion Picture Patents Trust agreed to what would become the standard: 35 mm gauge, with Edison perforations and a 1.33 aspect ratio.

Agfa began to produce motion picture film in 1913, but remained a largely local supplier until World War I boycotts of popular French, American and Italian film stocks allowed the UFA film studio to flourish, boosting Agfa's orders. All film stocks were manufactured on a nitrate film base, which is highly flammable. Nitrate film fires were virtually impossible to extinguish. A significant number of fatal accidents occurred in theatrical projection booths, where the heat of the projector lamp made ignition a possibility. Amateur filmmaking (home movies) slowly developed during this period. Kodak developed a heat-resistant 'safety base' for home projection.

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. Eastman Kodak introduced a non-flammable 35 mm film stock in 1909. The plasticizers used to make the film flexible evaporated quickly, making the film dry and brittle, causing splices to part and perforations to tear. In 1911 the major American film studios returned to using nitrate stock. More amateur formats began to use acetate-based film, and several, including Kodak's own 16 mm format, were designed specifically to be manufactured with safety base. Kodak released Cine Negative Film Type E in 1916 and Type F (later known as Negative Film Par Speed Type 1201) in 1917. As both of these orthochromatic films were no faster than previous offerings, the improvements were in granularity and sharpness.