International projectionist (Jan-Dec 1950)

developers dispense with some of these ingredients. A bewildering number of developing formulae are available for every type vof negative and positive emulsion. The following is a standard "MQ" (metol-quinone) developer for motion picture positives : Developer: Metol 2 oz. Hydroquinone l1/^ lb. Alkali: Sodium carbonate 7% lb. Restrainer: Potassium bromide 6 oz. Preservative: Sodium sulfite ^XA lb. Anti-stain: Citric acid 4 oz. Water to 30 gal. Development time about 5 min. at 68° F. The 'Fixing' Process Developing results in an image composed of black silver on unchanged cream-colored silver bromide. In time the remaining silver bromide would darken, and the picture would be all but lost. In order to render the image permanent, the unchanged silver bromide is removed, leaving clear film in its place. This process, called "fixing," depends upon the ability of a solution of sodium thiosulfate (commonly called "hypo") to dissolve away the unchanged silver bromide without affecting the reduced silver. A simple hypo fixer is unsatisfactory for several reasons. The chemicals brought over into it from the developing bath decompose it and cause it to stain the film; and the prolonged soaking of the film in the bath softens and frills the gelatine emulsion. These drawbacks are overcome by adding to (1) "hypo" an (2) acid to act as a "short-stop" and neutralize the alkali carried over from the developer, a (3 ) "sulfite" to prevent the acid from decom posing the hypo, and a (4) "hardener"' to tan the gelatine, and thus prevent frilling and blistering. Following is a complete fixer for motion picture positive: Hypo: Sodium thiosulfate 45 lb. Sulfite: Sodium sulfite 12 lb. Acid: Acetic acid (28%) 4 gal. Hardener: Potassium chrome alum 12 lb. Water to 30 gal. After fixing, the film is thoroughly rinsed and dried. Reversal Developing Reversal developing, a popular process for amateur cine films, is carried out as follows : (1 ) The film, after exposure in the camera, is developed in the ordinary way, but fixing is omitted. The negative image therefore consists of reduced silver and unaffected silver bromide. (2) The developed but unfixed film is washed and then bleached in a bath containing potassium dichromate acidified with sulfuric acid. Bleaching removes the black negative image (the reduced silver) and leaves the silver bromide. After bleaching the film looks very much like undeveloped film, but careful inspection will reveal a faint positive image made up of the pale yellow silver bromide. (3) To remove any stain and to restore the full sensitivity of the silver bromide, the film is next cleared in a solution of sodium sulfite. (4) After another washing the film is flashed by exposure to white light. (5) The final step is redeveloping in a regular developing solution. In order to preserve the proper contrast values, this should be followed by fixing and washing. The film, originally used in the camera as a negative, now has a High -vaulted emulsioncoating room at Kodak Park. Some idea of the size of this room and of the equipment therein may be had by comparing them with the size of the worker shown at the right. positive image and is ready for use in the projector. The silver images of ordinary blackand-white prints may be wholly or partly replaced by colored compounds or even dyes to give toned images. "Sepia" films are black-and-white prints toned to a rich chocolate-brown color. The two emulsions of duplitized color prints are dye-toned to the appropriate complementary colors. Combination toned and tinted prints, in which the dark portions of the image are one color and the light portions another color, were commonly used for pictorial and novelty reels in the days of silent motion pictures. The Printing Process Positive raw stock is supplied to film laboratories in 1000-ft. rolls which are securely wrapped to protect them from accidental exposure to light and packaged in round tins or fiberboard cartons. Because the quality of undeveloped emulsion slowly deteriorates with age, producing fog, film laboratories receive their raw stock in small quantities at frequent intervals and avoid accumulating too great a surplus. The raw film is unpacked from the shipping crates and placed in a storeroom from which it is issued to the printing-machine operators as needed. A printer is a machine designed to expose the positive raw stock to light which passes through the negative, thus forming an image of the negative picture or soundtrack on the emulsion of the positive. This is accomplished by drawing both films through a light-gate in which both films are kept in close contact, the emulsion side of one held firmly against the emulsion side of the other. "Reduction" and "expansion" prints cannot be made by ordinary contact printing, and so require the use of projection printers. A case in point is the printing of standard soundfilm positives from silent-picture negatives, the individual frames of which require a lateral displacement to accommodate the soundtrack area of the sound print, and also a slight reduction in size. Other common examples are the printing of standard 35-mm positives from sub-standard (16-mm and 8-mm) negatives, requiring enlargement of the individual pictures, and the printing of sub-standard positives from 35-mm negatives, requiring reduction. The two general types of printers used for printing the picture portion of films are designated as "continuous printers" and "step printers." The difference involves the manner in which the raw stock is exposed therein. In printers of the continuous type the (Continued on page 31) INTERNATIONAL PROJECTIONIST January 1950