Society of Motion Picture Engineers : incorporation and by-laws (1927)

Lubrication of Film — Crahtree and Ives 525 tation on the gate than "green" fihn, and this is usually attributed to the burnishing or polishing action of the aperture plate or pressure springs on the gelatin coating of the film. The burnishing effect produced by projecting the film in a Simplex projector ten times is very sHght, as shown in Fig 7 (magnification 540). This is a photomicrograph of the film surface in the region between the perforations. The lower half of the figure shows a portion of the film surface which was in contact with the aperture plate. The burnishing effect on the film surface is negligible. Fig. 7. Showing partial burnishing effect on fihn during projection. It is considered that traces of oil which are transferred to the film surface during the first projection are chiefly responsible for the increased ease of passage of the film on subsequent projection. It is obvious also that the moisture content and degree of hardening of the gelatin coating are important factors which determine the rate of formation of the incrustation in the gate. If the gelatin coating of the film contains an excess of moisture, it tends to soften and become "tacky" much more readily in the hot projector gate than is the case with dry film. This tendency of the gelatin coating to soften under the action of heat can be diminished by hardening during processing. However, excessive hardening tends to increase the brittleness of the fihn and is not to be recommended. 2. Apart from the condition of the film, the following factors relating to the conditions existing in the projector also determine the extent of the formation of the gate incrustation. A. The tension of the gate springs. This should be of the order