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Lubrication of Film — Crahtree and Ives 539
to another. The film roll was then rewound twice, during which time the oil was smeared over the surface with a cloth. After this treatment the film surface presented a mottled appearance. The reel was then projected immediately and subsequently three times each day.
After the first day objectionable oil spots appeared on the unwaxed sample. At the end of one week no oil spots were visible on any of the waxed samples. It was concluded therefore that paraffin wax although miscible with oil prevents oil spots. In order to prevent oil spots it is apparently merely necessary to fill up the crater-like depressions on the surface of the film.
A roll of toned film treated with candelilla wax and then splashed with oil was prepared over a year ago and projected at frequent intervals up to the present time. No oil spots have appeared on this film to date.
4. The Tendency of Surface Waxed Film to Accumulate Dirt and Develop Scratches on Projection
Sufficient data have not as yet been secured to determine the effect of the surface coating on the propensity of the film to accumulate dirt and develop scratches on projection in comparison with untreated film. A projection test was made by applying dirt to the projector gate and by throwing the film on a dirty floor and then projecting. No appreciable difference in the quantity of scratches or dirt accumulated on the film was noticed between surface waxed and edge waxed film.
Data in this connection are being secured by circulating reels, half of which are surface waxed and one half edge waxed, through various exchanges.
5. The Tendency of Surface Waxed Film to Retain Moisture It is well known that if the gelatin coating of motion picture film is deprived of its moisture content, the film tends to become brittle. The chief cause of brittleness of projected film is the loss of moisture as a result of repeated baking of the film in the hot projector gate.
It was considered that possibly the surface coating of wax might retard the evaporation of moisture from the gelatin, and this was tested by first humidifying a strip of film for one hour in an atmosphere at 90% relative humidity, surface coating one-half of the strip with wax, and then placing the waxed and unwaxed strips in a desiccator over night. No difference in brittleness of the two dried