Film Chemistry: "The Alchemist In Hollywood" ASC American Society of Cinematographers 1940

• published: 28 Dec 2011
• views: 13074

more at http://showbiz.quickfound.net/ "Explains chemical processes used in the motion picture laboratory. Diagrams and demonstrations of exposure, photochemical reactions, development, and printing." From the American Society of Cinematographers. Public domain film from the Library of Congress Prelinger Archive, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied. The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization. http://en.wikipedia.org/wiki/Photographic_processing Photographic processing is the chemical means by which photographic film and paper is treated after photographic exposure to produce a negative or positive image. Photographic processing transforms the latent image into a visible image, makes this permanent and renders it insensitive to light. All processes based upon the gelatin-silver process are similar, regardless of the film or paper's manufacturer. Exceptional variations include instant films such as Polaroid and thermally developed films. Kodachrome required Kodak's proprietary K-14 process. Kodachrome film production ceased in 2009, and K-14 processing is no longer available as of December 30, 2010. Ilfochrome materials use the dye destruction process. Common processes A black-and-white image showing a (monochrome) photograph being developed. All film and paper is treated in a series of chemical baths, which are closely monitored and maintained at a specific temperature and treatment time. Developer baths are most sensitive to deviations from the standard time and temperature of treatment; other baths are less sensitive. Black and white negative processing - The film may be soaked in water to swell the gelatin layer. - The developer converts the latent image to metallic silver. - A stop bath, typically a dilute solution of acetic acid or citric acid, halts the action of the developer. A rinse with clean water may be substituted. - The fixer makes the image permanent and light-resistant by dissolving any remaining silver halide salts. Fixer is sometimes called hypo, a misnomer originating from casually shortened form of the alchemist's name hyposulphite. Neither hyposulphite, hyposulfite, nor hypo is used to mean thiosulfate in modern chemistry. - Washing in clean water removes any remaining fixer. Residual fixer can corrode the silver image, leading to discolouration, staining and fading. The washing time can be reduced and the fixer more completely removed if a hypo clearing agent is used after the fixer. Film may be rinsed in a dilute solution of a non-ionic wetting agent to assist uniform drying, which eliminates drying marks caused by hard water. (In very hard water areas, a pre-rinse in distilled water may be required - otherwise the final rinse wetting agent can cause residual ionic calcium on the film to drop out of solution, causing spotting on the negative.) Film is then dried in a dust-free environment, cut and placed into protective sleeves. Once the film is processed, it is then referred to as a negative. The negative may now be printed; the negative is placed in an enlarger and projected onto a sheet of photographic paper. There are many different techniques that can be used during the enlargement process. Two examples of enlargement techniques are dodging and burning. Alternatively (or as well), the negative may be scanned for digital printing or web viewing after adjustment, retouching, and/or manipulation. † In modern automatic processing machines, the stop bath is replaced by mechanical squeegee or pinching rollers. These treatments remove much of the carried-over alkaline developer, and the acid, when used, neutralizes the alkalinity to reduce the contamination of the fixing bath with the developer.