International projectionist (Jan-Dec 1952)

A print on nitrate stock showing conflicting identifications printed through from a safety master positive and a safety duplicating negative. tionist relaxes his vigil against the fire hazard. For checking large reels made up of Eastman Kodak film only, the fluorescence test may be used. Eastman has introduced tiny amounts of normally invisible (clear) fluorescent materials into its safety base. When irradiated with "black light" (ultraviolet radiation with all visible wavelengths filtered out), Eastman high-acetyl safety film glows bright purple, whereas nitrate film appears black by comparison. However, we also have Du Pont safety film to reckon with (which at present is similar to the Eastman high-acetyl film in this respect), and likewise Ansco Color safety base. In addition, large quantities of the Belgian Gevaert high-acetyl safety film seem to be floating about, and this is not always fluorescent. The German Agfa film, once a great favorite in this country because of its consistently high physical and photographic quality, is now almost exclusively a behind-theiron-curtain product; so we need not worry about that except in very old prints. The actual splicing of high-acetyl safety film is a simple matter when good cements are used. The only trouble is that it takes about twice as long for a safety splice to "set" solidly than it does for a nitrate splice. This is because highacetyl base, practically the triacetate of cellulose, is very resistant to solvent liquids. Only a limited number of solvents attack it readily ; and most of these are too poisonous to be used in the projection room. The projectionist not only breathes the fumes, but he usually gets a bit of the stuff on his fingers, where cuts and minor abrasions assist the obsorption of poisonous chemicals into the bloodstream. So the bad actors in the chemical family don't get into filmcement bottles. Scraping the Splice Proper scraping, however, assists the "setting." After scraping the stub in the usual manner, roughen the surface of the base, just as most projectionists have always done with nitrate film. Emery cloth of the finest grade may be used; and if the splice is afterward brushed with a clean piece of cloth, there isn't much danger of gritty particles getting into the projector. Some projectionists prefer razor blades; and this writer swears by a piece of beryllium copper ground to a razor-sharp edge. Now, just what is the reason for roughening the stub? It increases the surface area enormously, providing more exposed base for the film-cement to act upon. Most projectionists don't need this advice; but here we go again. Apply the cement you are using with one or two strokes of the brush — no more. Clamp and allow about 10 seconds for the splice to set. (Only 5 seconds are needed for nitrate film spliced with regular nitrate cement.) And if the splices seem to be especially slow in setting on certain chilly days, first warm up the splicing gadget on a hot radiator or with an electric heating unit (but remove the splicer from the rewind bench to do this). Film Cements This brings us up to the film-cement itself. What's it made of? How does it act on the film? To answer the last question first, a film-cement is merely a solvent which dissolves the film base. It acts upon the surfaces of the stubs and welds them together. It is not a glue. The filmbase material itself is the glue. In practice, however, the solvent liquid (which may be composed of several solvent chemicals mixed together) may be thickened by dissolving a little of the proper film-base material in it — nitrate base in the case of nitrate film-cement, safety base in the case of safety film-cement, and safety base with a trace of nitrate base in an effective "double-purpose" film-cement. Projectionists do not like a "thin" cement. If the cement is too watery, it does not remain on the stub where it has been applied, but runs off the edges of the film, or creeps underneath the film-holders to soften the film exactly where we don't want it softened. A syrupy consistency works best because the cement then sticks to the stub where applied and does not "soak up" half a frame of film. If too thick, however, the cement may not penetrate the stubs sufficiently to give a good weld. High-acetyl Cements High-acetyl safety-film cement is but a trifle more complicated in practice than nitrate cement because, while there are many simple and inexpensive solvents for nitrate base, only a few work well with high-acetyl base — and some of these are rather weird. In fact, a descriptive list of feasible triacetate solvents makes mighty short and dismal reading. First, however, let's consider two very good solvents for nitrate base, i.e. banana oil and acetone. Banana oil (amyl acetate) has little or no effect on high-acetyl base. This chemical, therefore, should not be used in any cement intended for safety film. Acetone, even though failing to dissolve large quantities of safety base, softens it sufficiently to give weak to moderately strong safety splices. But splices made with pure acetone buckle so badly An ultra-violet lamp used for examining a roll of film to determine whether it is on fluorescenttreated safety base. (Photographed with white light.) INTERNATIONAL PROJECTIONIST November 1952