Richardson's handbook of projection (1930)

1004 HANDBOOK OF PROJECTION FOR even pass entirely unnoticed, but in the process of rewinding, repairing, et cetera, films are handled a great deal, and if the men so handling them have dirty, oily hands, the results will soon become very apparent in the reproduced sound. Moral: Sound projectionists should make it their invariable practice to remove any oil or dirt from their hands before handling sound films. Of course it is true that that rule should be adhered to by all projectionists, silent or sound, but the point is that with sound it becomes imperative. Dust in the air in a projection room also is very, very bad in any event, but where the films carry a sound record it should be kept to the absolute possible minimum. If there is dust in the air it is inevitable that some of it will be deposited on the films, and that in the process of projection and rewinding — particularly the latter — scratches on the film surface, including the sound band, will result. Such scratches usually are minute in size, but they nevertheless set up what is called "surface noise," which is a sort of grinding sound when reproduced by the horns. It is strongly recommended that projection room floors be not swept with a dry broom. Before sweeping, if a broom is used, hold it under a water faucet a moment, or dip it into a pail of water. This will appreciably reduce the resultant dust. Never leave film exposed while sweeping the projection room floor. It is strongly recommended that the management provide a good vacuum cleaner, with suitable attachments, and that at least once each week all parts of the