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CLEANING LIQUIDS FOR MOTION PICTURE FILM
J. I. Crabtree and H. C. Carlton*
IT IS necessaiA^ to clean motion picture film at various stages in its progress from the laboratory to the theatre to remove:
1. Dirt on the base side of negative or positive film;
2. Dirt or grease which may accumulate on negative film during printing ;
3. Dirt and oil which accumulates on positive film during projection.
1. AATien processing in the laboratory by the reel and tank system, if all excess water is not removed from the film pre\'ious to drying, any dissolved salts present in the water supply remain on the film after evaporation of the water. The residual salts are usually only visible on the base side of the film because on the emulsion side they have an opportunity to diffuse within the gelatin coating during dr^dng.
It is necessary to clean the back of the dried film either by wiping with a damp chamois while on the dr^dng reels or by passing the film through a cleaning machine. Such treatment is unnecessary in the case of positive film if all excess water is removed previous to placing on the drying reel by thorough wiping or squeegeeing.
In the case of negative film it is customary to wind it with the emulsion side downward onto a wooden drum covered wdth cloth when the base side may be cleaned without danger of injuring the image. The cloth should be removed from the drum at frequent intervals for cleaning.
A suitable cleaning liquid for the above purpose should possess the following properties:
(a) It should be capable of dissolving traces of inorganic salts and should also dissolve or emulsify grease and mineral oil;
(b) It should be sufficiently volatile and should not cause the gelatin side of the film to swell in a period of several seconds if it accidentally has access to it;
(c) The liquid should not affect the physical properties of film with safety or nitrate base or remove the color from film with tinted base.
A suitable mixture fulfilhng the above conditions is the following :
* Research Laboratory, Eastman Kodak Company.
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