International projectionist (Jan 1961-Dec 1962)

16 . 10 i.l -p < *N v \ V\ TRIArFTATF-RA<;F \nit i~» • s~ r>r luue ^r \ 1 Time ►" (Under ■severe conditions) FIG. 3 — The flexibility, toughness, and pliancy of triacetate safety film are practically permanent characteristics of this type of stock, whereas the initially superior characteristics of nitrate film rapidly deteriorate with age and projection use. Barring scratches, torn perforations, and other mechanical damage, acetate prints remain usable long after nitrate prints subjected to similar conditions of use have become brittle, shrunken, and dangerously unstable. thousands of reels of nitrate negatives and master positives in storage. Although triacetate safety film is almost completely non-inflammable, it resembles nitrate in its sensitivity to abnormal relative humidities. Just as extremely dry air causes nitrate film to become brittle, so does dry air cause acetate film to become brittle and liable to crack if sharply bent. Dry film also has a tendency to curl, especially if it has been wound too tightly in small rolls or upon small-hub 1000ft. reels. As a rule, however, dry film loses some of its curliness and regains its tough pliancy when exposed to normally moist air month. l50%-60% R.H..) for about a Shrinkage Accelerated by Moisture Also like nitrate stock, acetate film is harmed by excessively high humidities. It doesn't decompose, burn, or explode as nitrate does, but moisture causes it to shrink. Shrunken film is noisy in the projectors and gives weaving, unsteady images on the screen. Many film workers fail to realize that excessive moisture causes film to shrink. Exhaustive studies made by Eastman Kodak scientists reveal conclusively that the permanent shrinkage of some motion-picture films is approximately twice as rapid at 90% R.H. as it is at 60% R.H. The initial effect of moisture on film is to cause it to swell. This is observed when the film is immersed for several minutes in developers and other solutions during processing. Now, the initial longitudinal swelling of the film reverses itself and changes to shrinkage during the drying operation. The shrinkage of freshly processed film is usually slight because the processing solutions are cool and because the film is wet for too short a time for the base to absorb much moisture. The subsequent shrinkage is much more severe when the film has been stored for weeks or months in highly humid air and then brought into an atmosphere of normal relative humidity. High temperatures accelerate all of the adverse changes in film induced by high relative humidities. That is, if the emulsion spoils and the base shrinks at a certain rate at 80 °F. and a R.H. of 90%, the deterioration and shrinkage will occur very much faster at 100°F. and the same high R.H. Indeed, motion-picture film is very quickly ruined by the high humidities and temperatures of the tropics, and may even become moldy and sticky in camera magazines and projection-room storage bins. The ideal storage conditions for motion-picture film, both negative and positive, unexposed and processed, are low temperatures (50°F. or lower) and normal relative humidities (not less than 50% or more than 60%). Do Not Experiment with Prints! All attempts to restore or introduce moisture to the base material of motion-picture film should be scrupulously avoided by the projectionist. Prints should never be "steamed." Prints should never be stored over open water in the film cabinets. Film should never be kept in cans having glycerinemoistened "humidifying blotters." Do not place camphor blocks or crystals in film cans or storage bins. There is some evidence that camphor protects nitrate film against undue shrinkage and brittleness; but this writer does not know of any responsible tests anent the effect of camphor vapor on triacetate stock. It is entirely possible that the fumes of evaporating camphor retard the loss of the plasticizers incorporated into the film base during its manufacture, thus preserving the original toughness and pliancy of the film. Camphor was used for this purpose in the old 3-strip Technicolor cameras which exposed three separate panchromatic negatives on nitrate base. Neither 3-strip cameras nor nitrate negative are used today. If acetate film actually does absorb camphor vapor, there is conceivably a danger inherent in the use of this volatile plasticizer. If the edges of the roll of film take up more camphor than the middle areas, there is a risk of dimensional distortion. Until conclusive tests have made and the use of camphor approved as a film preservative by a responsible film manufacturer, we must refrain from recommending the placement of camphor blocks in film-storage bins. Our conclusion is a simple one, namely, that the best storage treatment for film in the projection room is a liberal application of common-sense. All cans and boxes containing film, shipping cases, and storage bins and cabinets should be placed in the coolest, driest part of the projection room or rewind room. Film — not even seldom-used "emergency prints" — should be kept in damp cellars or anywhere near hot radiators, arc rheostats, rectifiers, etc. The relative humidity of the air may be considered satisfactory for film storage when it is comfortable to the projectionists, i.e. neither too humid nor too dry. It is only necessary to keep in mind the simple fact that excessive moisture in the air softens and harms the emulsion of film and accelerates shrinkage of the base material, while excessive dry air makes film curly, brittle, liable to break in the projectors, and retentive of frictional electricity which may produce static crackling and snapping noises in the sound reproduction. Treatment of prints with water vapor, we repeat, is troublesome, usually ineffective for the intended result, and possibly harmful. The physical condition of theatrerelease prints during their exhibition life is much too vital to the welfare of the entire motion-picture industry to be jeopardized by injudicious experimentation and untested treatments. An irreparably ruined print can never be restored. iP International Projectionist May 1962