International projectionist (Jan-Dec 1950)

bottom rollers to form many hundreds of long loops which bring the emulsion into effective contact with the current of warm, dust-free air which is continuously supplied to the chambers by special air-conditioning equipment. From the drying cabinets the film goes to a takeup assembly at the end of the machine to be wound up on 1000-foot reels. The swelling and shrinkage characteristics of film stock are important considerations in machine developing. The older types of safety film (cellulose diacetate and acetopropionate) underwent considerable swelling, or longitudinal expansion, when wet, causing the film to slack off the bottom rollers in the processing tanks, and it shrank very rapidly when drying out, resulting in excessive tension and distortion of the film in the drying cabinets. The newer high-acetyl safety film swells only a little more than nitrate film by absorption of water. Moreover, the rate of shrinkage of high-acetyl film is comparatively slow, eliminating undue tension and straining of the film during the final stages of drying. The greatest care is taken in the preparation of the processing chemical solutions. A single mistake in mixing these might easily result in spoiling hundreds of dollars' worth of positive raw stock or, worse, long lengths of precious negative. In large laboratories, solutions are mixed in tanks built just for this purpose, and are transferred to the tanks of the developing machines by pumps. The developer is frequently tested with sensitometric control strips (frequently inserted in the leaders of the film stock1) and corrected if any departure from standard strength is noted. It is customary to mix fresh developer every day for both negative and positive processing. Hypo (fixer) is mixed fresh daily for negatives, but is often used two days in succession for positives, the dissolved silver being removed from it electrolytically and more sodium thiosulfate added to maintain constant strength. The recovery of silver from spent fixing baths is a source of con 1 The placement of densitometric strips in the leader negatives for the purpose of checking the development of prints is understandably a desirable practice. But the projectionist is grossly imposed upon whenever such strips are inserted in the main portion of SRP threading-up leaders. Your Best Buy . . . U. S. SAVINGS BONDS siderable revenue to film laboratories. Certain photochemical troubles are sometimes encountered in the developing process, particularly in the development of the more rapid panchromatic negative stocks. One of these is a "halo" effect produced at the edges of dark objects in the negative image. This is due to the release of bromine from the reduced areas. In some instances the bromine is carried along by the film to produce streaks which may be either light or dark, and resembling "travelghost" when light. Another difficulty is the production of a 96-cycle hum in the sound by droplets of developer adhering to the sprocket holes of the film and spreading into the soundtrack. This trouble, discussed exhaustively in a number of technical papers, has now been largely overcome. Preparing the Release Print The 1000-foot reels of processed and dried film are sent to the inspection room, where each reel is projectiontested. Defects are indicated by paper slips placed on the film in the takeup magazine of the projector while it is running — a procedure familiar to all projectionists — and the defective portions are later replaced with reprints. The prints are then ready to receive "lubrication" in the film-waxing room. The purpose of this treatment is to minimize damage caused by the "sticking" of new prints during the first few projections with high-amperage carbon arcs. Even though dry to the touch, the emulsion of a "green" print contains a considerable amount of moisture, the presence of which makes the emulsion soft and amenable to damage. The intense heat of the projector gate further softens the emulsion, causing it to rub off and accumulate on gate runners, where it forms hard deposits which result in a variable "drag" on the intermittently-moving film. At one moment the holdback is so great that the film perforations are torn; and the next moment the film "lets go" and overshoots on the intermittent sprocket. "Sticking" is evidenced by a violent chattering of the film, and, when severe, in an excessively jumpy picture on the screen. In the standard method of film lubrication, a thin coating of carnauba wax is applied to the perforation margins on the emulsion side of the film. In another method, a very dilute solution of carnauba or similar wax in carbon tetrachloride is applied all over the emulsion side, and a radically different (and more expensive) process coats the emulsion with a thin layer of nitrocellulose lacquer. The finished reels — still of the standard laboratory length of 1000 feet — are packed in tins, (the same cans in which the raw stock came) and released to the exchanges, where reels of the longer film subjects are "doubled up" and wound on 2000-foot shipping reels for distribution to the theaters. [To be Continued] How Many? Was this copy dog-eared when it came to you? How many men read it ahead of you? You would receive a clean, fresh copy if you had a personal subscription — and you wouldn't have to wait — you would be first to read it. Use coupon below. INTERNATIONAL PROJECTIONIST. 19 West 44 St., New York 18, N. Y. D 1 year— 12 issues— $2.50 D 2 years — 24 issues — $4.00 Foreign and Canada: Add 50c per year. Enter my subscription for Name Address City State 34 INTERNATIONAL PROJECTIONIST January 1950