Richardson's handbook of projection (1930)

1006 HANDBOOK OF PROJECTION FOR the problem is to remove the dirt without causing even very small, faint scratch marks. Any scratches at all in such a sound track, no matter how minute, will cause "surface" or "ground" noise at the horns or loud speakers. Because of the difficulty of removing dirt, particularly oil, without applying sufficient pressure to cause some scratching, I hesitate to advise as to just what method may be best, preferring to suggest that you, knowing the evil effects of scratch marks, use your own good judgment. I would, however, suggest that when cleaning is attempted, only some very soft material should be used for the pad through which you draw the film, and that the material should be changed frequently, because it will of course collect the dirt in its surface. I am of the opinion that, because of the difficulties of cleaning without injury to the sound track, the projectionist is justified in refusing to do it at all. Cleaning is a duty of the exchange. Their contract with the theatre automatically presumes film in first class condition to project — "first class" according to the class of service the theatre is paying for. Regardless of the class of service, however, it may be fairly assumed that it is a part of the duty of the exchange to maintain the films in as perfect a state as the class they represent will permit, and while the fact that a theatre takes cheap service may justify mechanical imperfections which cannot be avoided, such as bits removed in making splices, it does not justify the supplying of dirty films, because that imperfection is unnecessary in that it may be removed by the exchange.