International projectionist (Jan-Dec 1955)

svrup by dissolved nitrate base or celluloid. Note that nitrate cements were composed of inexpensive and relatively nonpoisonous ingredients. Their "setting" action was swift, seldom requiring more than 4 or 5 seconds for a perfect splice. Triacetate safety-film base, on the other hand, is resistant to the action of the common nitrate-base solvents. Safety film may be spliced with glacial acetic acid to which a small amount of chloroform has been added, but this pungent mixture is so corrosive to the metal parts of splicing blocks that it is intensely disliked by projectionists. The best solvent for triacetate base which is not too poisonous to be used ii: the projection room is a colorless liquid of faint, ethereal odor known as "dioxane." All good safety-film cements contain 50% or more dioxane by volume, the remainder being methyl acetate, acetone, alcohol, or some compatible solvent. Solvents such as methylene chloride, ethylene chloride, and especially tetrachloroethane, are too toxic to be used with safety in film cements. It is noteworthy that the effective tiiacetate-film cements — the ones containing 50% or more of dioxane, and no chloroform, which does not dissolve nitrate base — are also satisfactory for splicing the older kinds of safety film and nitrate film. Such cements are accordingly "all-purpose" cements, and are recommended for all types of motionpicture film, excepting certain non-cellulose films now being tested in theatres but not yet in general use. Focusing Difficulties No sooner had triacetate safety film bowed in the theatre field than numerous complaints of focus difficulties emanated from projectionists. The new film base was blamed in nearly every case. Investigation revealed that the rigidity cf safety film was somewhat inferior to that of nitrate film, and that stresses and strains deform triacetate film more readily. This was, and to some extent still is, especially true when the film is subjected to the heat of the projector gate and arclamp beam. Although nitrate film becomes very brittle when heated, safety film buckles and warps out of shape to a greater extent, particularly if simultaneously subjected to mechanical stress. Recent improvements in the triacetate base, however, have resulted in a safety film which is practically equal to nitrate film in rigidity and tearstrength, and certainly superior to nitrate film in aging characteristics. Tri acetate safety film does not become so brittle with age and repeated use, it does not shrink nearly as much as nitrate film, it withstands wear better when cold, and, unlike nitrate film, it never disintegrates spontaneously. Practically all the credit for the development and commercial production of a successful safety-film base must go to Eastman Kodak Co. The task was far more formidable than most people realize, for it was known at the outset tli at any new safety film must be far superior to the old diacetate and acetopvopionate safety films to win acceptance in the 35-mm field. Thanks to Eastman, film is now not only safe but also permanent. Nitrate film literally rots (and sometimes spontaneously explodes) after 40 to 60 years of storage. Triacetate film will likely endure for a millennium; and precious negatives need never be lost beyond recall. Even though some of the difficulties in focusing safety film must be attributed to failure of the film to lay flat over the aperture, it is definitely known that much of the trouble was caused by inefficient printing and by the use of duplicate negatives printed from shrunken master positives. Certain reissued pictures, it was discovered, were printed from dupes made from old re ^rrolldau Lureetinad from ^^ PHILIPS * To projectionists everywhere go our warmest greetings coupled with the hope for a continuance of the friendly relationship begun with the introduction of the Philips 35 and 70-mm all-purpose projector used in the Todd-AO production of Rodgers & Hammerstein's "Oklahoma!" PHILIPS — the finest in motion-picture projection equipment. Represented by: NORTH AMERICAN PHILIPS CO., INC. 100 East 42nd Street New York 17, N. Y. 22 INTERNATIONAL PROJECTIONIST • DECEMBER 1955