International projectionist (Oct 1931-Sept 1933)

July 1932 INTERNATIONAL PROJECTIONIST FIGURE 1 FIGURE 2 FIGURE 3 Fig. 1 : Photomicrograph showing appearance of surface of motion picture film by reflected light. Fig. 2 : Photomicrograph showing (A) untreated film, and (B) effect of coating film surface with wax and then polishing. Fig. 3: Showing burnishing effect on film during projection. Upper half — unbumished; lower half — burnished treated film the oil spots are very objectionable on projection; and (d) Extensive tests have shown that the film has a much less tendency to accumulate ground noise with use. If a soft wax coating such as paraffin is used for the surface treatment, it is apt to attract dirt; so it is preferable to use very hard waxes which, in turn, are not the best lubricants. The necessary lubrication is provided by applying a lubricating wax or oil to the edges as described hereafter. The above double treatment of film is relatively expensive, and due to the advent of biased recording and the greater care with which film is handled, ground noise is not as serious a factor as was previously the case. Lubricating Film Edge 2. By treating the edges of the film with a suitable lubricant such as paraffin wax or lubricating oil. A number of years ago it was customary to apply a thin line of wax along each edge of the film surface and between the perforations by means of a S.M.P.E. Symposium on Waxing Mr. Crabtree: I noticed that the committee regards the waxing of film as undesirable. With the early method of \fraxing, when the film in the waxing machine became too cold, it accumulated on the blades and was applied too thickly to the film. It then caused trouble at the projector gate. But I should like to recommend a change that has been made — to use a solution of the wax, the concentration of which controls the amount of wax applied, so that it is impossible to apply too much wax unless the solution is too concentrated. I made a survey of the different laboratories in New York, and found that 95 per cent of them are using a solution of wax for edge waxing. To what extent is wax accumulating in the gates of projectors today? Does the accumulation consist of wax, dirt, gelatin, or a mixture of these? What is wrong with the present method? Mr. Finn: It doesn't require extended research to uncover the fact that waxing of film is, to say the least, undesirable. I don't think it presumptuous to state that a majority by far of projectionists do not desire that film be waxed — that is, as waxing is now done by certain laboratories. Mr. Richardson: The chairman of the Committee is a supervisor of projection, and everyone on the Committee engaged in practical projection made the statement that no method of waxing has yet been used that would not result in some deposit in the sound gate. Yesterday we were told that waxing of film to be used in the Navy's projectors is taboo. It was said that there is no waxing process that is not objectionable. Mr. Edwards: I agree with Mr. Richardson. Our experience in a firstrun film house has shown that it is necessary to take out the sound gate and clean out the accumulation of wax after every running. If this is not done, we soon find that we have a "frozen" film in the gate. Mr. Crabtree: Yet 95 per cent of the laboratories are using this process of waxing. I feel that if trouble is being experienced, the laboratories are using a stronger solution of the wax than is recommended. Mr. Edwards: It is quite possible that the fault lies not so much in the process as in the application of the process. Probably as much care is not taken in applying the wax as was intended by the inventors of the system. We have to dig out the wax from the grooves in the rollers up to the tenth run. If neglected for one reel, we often find that the heat of the plate will melt the wax and the film will adhere to the gate. machine similar to that illustrated in Figure 4. This machine consists essentially of two parallel thin steel disks separated by a distance of 1 3/32" rotating in a vertical plane. The disks dip into a bath of molten paraffin wax and apply the wax to the film at their upper edge. The quantity of wax applied is controlled by the thickness of the disks, the temperature of the molten wax, and the rate of travel of the film. The above method of lubrication is entirely satisfactory, providing the wax is applied correctly. However, if the temperature of the molten wax is not sufficiently high during application, too much wax is applied by the disks and this does not solidify sufficiently before the film is rewound. This causes the wax to cement the edges of the film convolutions, so that on rewinding, particles of wax are torn away from the film and these tend to incrust on the picture area, causing spots and splotches on the film. Particles of wax also tend to lodge on the sound track with deleterious effects and they likewise accumulate in the reproducer aperture, thereby diminishing the volume of reproduced sound and, in some cases, cutting off the sound completely. Another very serious danger resulting from the application of an excess of wax arises if the projector is threaded while hot with film coated with an excessive quantity of wax. As the projector cools, the wax solidifies and holds the film so tightly that on starting the projector, the intermittent sprocket may tear out the perforations instead of pulling the film down through the gate. Also, since the fire shutter opens immediately when the projector starts, more or less film is apt to be burned up if the film does not start to move down promptly past the aperture. Repeated tests have shown, however, that this trouble is not likely to occur