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530 Transactions of S.M.P.E., Vol. XI, No. 31, 1927
Tests were then made to determine the quantity of wax which could be put on the film before it could be classed as waxed film, which would cause trouble by sticking in the projector. Several strips of film were prepared by waxing on the Eastman waxer, once, twice, three times, etc. In this way film coated with a known quantity of wax was obtained. The projector was then thoroughly cleaned, heated for thirty minutes, and threaded first with film which had been waxed once and allowed to cool. This procedure was followed with the film waxed twice, three times, etc., successively until indications of sticking in the gate were discovered. Repeated tests showed that trouble was not likely to occur unless the film was w^axed for five or six times and therefore contained five or six times the quantity of wax normally applied by the Eastman waxer.
The above experiments serve to emphasize the importance of applying the correct quantity of wax to the film and of remo\dng at very frequent intervals any wax which accumulates on the projector gate.
Lubrication of the Entire Gelatin Surface of Motion Picture Film
At the outset it was considered that by coating the entire gelatin surface of motion picture film with a thin layer of a suitable lubricant, many of the objections to edge lubrication would be overcome. Also, if the coating could be made impermeable to oil, trouble from oil spots would be eliminated likewise.
The idea of lubricating the entire gelatin coating of the film is by no means new. A large number of patents have been granted for particular lubricating formulas which include the use of tallow, lard, spermaceti, stearic acid, sodium stearate in methanol, oil of turpentine, olive oil, cotton seed oil, linseed oil, petrolatum, a suspension of gypsum in methanol, beeswax, and paraffin wax.
Before the commencement of the experiments described below, the Dworsky Film Mfg. Co. was supplying a filmbufl&ng machine shown in Fig. 9. This consists essentially of a series of four or five cloth buffing wheels similar to those used for polishing electro-plated metals, which buffers rotate at a high speed in contact with the gelatin surface of the film. The film is pulled through the machine by means of two rubber covered rollers of the laundry wringer type, the machine being entirely sprocketless. (The lower application roller attachment was not originally fitted to this machine). Usually a little tripoh