Movie Makers (Jan-Dec 1945)

■V 91 b The character of splices and how to make them FREDERICK G. BEACH, FACL A SOMEWHAT technical operation that almost every amateur filmer must perform is film splicing. Why this joining of two film pieces is called "splicing" will always remain a mystery; for it is a welding operation, pure and simple. A further misnomer is given to the fluid used for the operation, which is called film cement. A cement is an adhesive, and the so called film cement is in no sense an adhesive. When film ends are joined in the conventional way, they are flowed together in much the same manner that metals are joined with a high degree of heat and the application of a small amount of the molten metal. The film joining fluid is a solvent which dissolves the base and causes two pieces to flow together as one. The solvent is made a part of the joint: it does not remain on the joined surface as would glue or other adhesive. To learn the technique of film splicing, it is necessary to understand the structure of the film. The base, or foundation, for 8mm. and 16mm. movie film is a clear ribbon of non inflammable cellulose acetate. It looks like a thick cellophane tape, although it is not of the same chemical composition. The transparent ribbon is useless as a photographic medium until it is coated with the light sensitive silver salts suspended in an emulsion of gelatin. Coated in a tissue thin layer, this emulsion converts the ribbon into a film capable of registering a photographic image. Before the emulsion is coated on the clear base, it is necessary to place a binder coating on the base's surface. This coating enables the emulsion to adhere to the base more firmly. Thus we find that two separate layers of materials are placed on the base, both of which must be considered when two films are to be joined. Since film cement is a solvent for the base only, it will not attack or soften the gelatin emulsion or the binder coating beneath it. These two layers must be completely removed before a weld can be made. An enlarged diagram of the film is shown in Fig. 1. To make film splicing easy and reliable, it is necessary to use a splicer or, as an engineer would call it, a jig, to hold the parts in alignment while they are being joined. The splicer is so designed that it will grip the two pieces of film and hold them in fixed position in relation to each other. The first operation in using a splicer is cutting. A slight overlap is necessary in order to make the joint and to give sufficient bearing surface for the solvent to act. The width of this overlap will vary somewrhat according to the make of splicer. The narrowest is about one sixteenth of an inch, in a splicer made for use with negative film. Many 8mm. filmers have found this width to be ideal, because it makes such a narrow overlap. Typical 16mm. and 8mm. film splicers produce laps that run one tenth of an inch or more in width. Their respective merits are purely a matter of personal opinion. After the ends of the films have been cut properly, the next step is to remove all traces of emulsion and undercoating from one piece of film where the other will touch it in overlapping. Since the film is always placed in the splicer with the emulsion side up (for normal reversal film), one piece must be so scraped that the shiny, or base, side of the other will be clamped on the [Continued on page 104] • Fig. 1. If a small section of movie film were to be magnified to a great size, we should see that the film is made up of more than one layer. In this illustration, the thickness of the various layers is exaggerated. FILM BASE WITH EMULSION AND BINDER COMPLETELY REMOVED * Fig. 2. To make a welded splice, all of the two top layers — emulsion and binder— should be completely removed. The base side of the other film may have picked up dirt or oil in projection and handling. They must be removed before a good weld can be made. _rAfmLr'y~ FILM BASE WITH^2^^^^ t£f / EMULSION AND BINDER^\ NOT COMPLETELY REMOVED Diagrams courtesy Eastman Kodak Company • Fig. 3. If any emulsion or binder remains on the base in the area where the splice is to be made, a good weld will not result, and the splice may not hold. Small specks of emulsion or binder can be removed by a fine abrasive.