American cinematographer (Jan-Dec 1928)

Ten AMERICAN CINEM ATO GRAPHER February, 1928 (B) An entirely satisfactory mechanism for applying the wax solution is shown in Fig. 11. The film Fig. 11 — Application roller for applying wax solution. passes gelatin side downward over the polished aluminum roller Rl (about 2M: inches diameter) which dips in the wax solution at room temperature in tank T to a depth of about XA inch. The excess wax solution is removed from the surface of the roller by means of a "doctor" S consisting of a sheet of thick paper on ordinary motion picture film. This leaves an extremely thin layer of wax solution on the roller which is applied to the film surface at P. The friction between the roller Rl and the film is sufficient to drive the roller Rl without danger of slippage. This friction can be increased by lowering the idler roller R2 in relation to roller P. The latest type of Dworsky buffing machine is shown in Fig. 12. This is shown fitted with application Fig. 12 — Improved type of waxing and polishing machine. rollers as first developed by the authors. It is suggested that the single application roller shown in Fig. 11 be fitted to the new type machine. Manipulation Details Although at first sight the waxing machine appears somewhat complicated, it is very simple to operate, does not get out of adjustment, and requires little or no attention other than changing of the reels. The level of the wax solution is maintained constant by means of an inverted bottle or can fitted with a tube dipping into the tank of liquid. The depth of the liquid is then at all times equal to the distance between the tube orifice and the bottom of the tank which holds the liquid. The film travels at the rate of six to twelve inches per second, the six inch speed giving a more desirable polish to the film surface. A roll of one thousand feet is, therefore, waxed in from fifteen to thirty minutes. About two ounces of liquid are required per one thousand feet of film providing the exposed surface of liquid in the tank is covered as far as possible to prevent evaporation. The rubber rollers at A (Figs. 9 and 12) should be celaned at intervals by holding a cloth moistened with carbon tetrachloride against the surface so as to remove tracts of lint. After waxing it is desirable to rewind the film while passing it between the folds of plush so as to remove occasional particles of lint which tend to adhere to the film after polishing. It might be considered that the film would ignite from the heat developed by friction perchance the film should remain stationary in contact with the rotating buffers. Tests indicated that the film did not fire after remaining stationary in contact with the buffers for thirty minutes. Choice of Waxes and Solvents The following waxes were tested: beeswax, cantol wax, candelilla, carbnauba, Japanese, Johnson's floor wax, montan, hard paraffin, and Simoniz wax. The choice of suitble solvents is somewhat limited because as pointed out in a previous paper,2 many 2. "Film Cleaning Liquids for Motion Picture Flm" by J. I. Crabtree and H. C. Carlton, Trans. So. M. P. Eng., No. 30, 277 (1927). solvents have a tendency to attack the silver image and are therefore unsuitable. The three solvents, benzene, gasoline, and carbon tetrachloride were used in the preliminary tests. Since carbon tetrachloride is non-inflammable and when pure has no harmful effect on the film, this solvent was used exclusively in the later tests. Properties of Motion Picture Film With a Coating of Wax over the Entire Gelatin Surface 1. The Projection Life as Compared with Edge Waxed Film. Comparative measurements were made on the projection life of the various samples of waxed film as follows: The ends of six-foot length of each sample of film were spliced together so as to form a loop and this was run continuously through a Powers projector maintained as nearly as possible under standardized conditions. The gate spring tensions were checked at regular intervals, and the machine otherwise maintained in first class condition. If any incrustation tended to form in the gate, this was indicated by a distinctive noise and the incrustation was at once removed. The number of times which the film passed through the machine was recorded by a counting device and projection of the film was continued until the perforations became torn to such an extent that the film would no longer pass successfully through the machine. Assuming a basis of 100% projection life for normally processed film which was not treated in any way before projection, the results of tests with fiums lubricated over the entire surface with various waxes were as follows: Nature of Wax or Oil Solution in Carbon Tetrachloride Projection Life Plain film (untreated) 100% 10 Montan 1% 77% Montan 5% 94% Turpentine 100% ( Continued on Page 27 )