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76 Transactions of S.M.P.E., August 1925
Prevention of Camera Static
The only certain method of insuring the absence of static markings is to prevent the generation and accumulation of the static electricity in the first place as follows:
1. By removing all sources of friction. Negative film which shows camera static markings generally also shows bad abrasion marks. Of the various parts of the camera the gate is responsible for most of the abrasion.
When making titles directly onto positive film in the camera the emulsion tends to scrape off onto the metal tracks where it builds up excressences of hardened emulsion which retard the passage of the film and incidentally cause static as a result of the increased friction. By glueing a small strip of oiled chamois on each side of the film track at its upper edge the passage of the film is facilitated and abrasion of the emulsion and the attendant static is prevented.
Film loops which are too long cause the film to rub either against itself or the side of the camera with the possible generation of static.
2. By making all camera parts conductors of electricity. As explained above, when film is rubbed with a conductor such as a metal, a minimum of static is produced especially if the metal is in electrical connection with the rest of the camera or is * 'grounded." Glass, hard rubber, varnished or lacquered metallic surfaces, silk and velvet should, therefore, be avoided whenever possible in camera construction, while the gate and sprockets and as far as possible every part of the camera should be of metal.
3. By rehumidifying the film. Negative film which is stored for considerable periods in a dry atmosphere loses moisture, but may be rehumidified by rewinding loosely and storing for about 12 hours in a humidor, consisting of an enclosed box containing either a sponge or other absorbent material saturated with water. A simple humidor may be constructed by soldering together two motion picture film cans bottom to bottom, perforating the now common partition and placing saturated blotters in one of the compartments. The loosely wound film should then be placed in the empty compartment and allowed to remain for about 12 hours at 70 to 75° F. The film should not be allowed to remain for too long a period in the humidor, especially at high temperatures (80 to 90° F.), otherwise moisture spots are liable to be produced on the emulsion.^
The practice of placing a moistened sponge in the camera is of no value if the film is run through quickly, but if the sponge is allowed to remain in the loaded camera for one or two hours the film has more opportunity to absorb water and may be less liable to develop static markings.
4 By conducting the products of combustion of an alcohol lamp into the camera chamber. Since the products of combustion of alcohol contain water vapor, the lamp has a two-fold effect of humidifying and ionizing the air which as explained above tends to prevent static.