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comes from the machines and is wound in rolls. Samples are then taken from strategic points in the roll and subjected to tests with specially designed instruments which determine tensile strength, elasticity and resistance to tearing and bending. The base material, if it is up to standard in every respect, is then ready to be coated with the emulsion (tiny particles of light-sensitive silver bromide suspended in gelatine) which has been prepared in the meantime, coated experimentally, and subjected to the most exacting chemical and sensitometric tests before it has been approved for coating on a large scale.
During the coating operation, film is constantly watched by workers who can almost see in the dark, from long experience working under the barely perceptible illumination permitted. In producing high speed panchromatic materials, the entire coating process must of course be conducted in total darkness and practically no visual inspection is possible at this stage. When coated film has dried, samples are immediately measured for emulsion thickness, while other samples are subjected to sensitometric tests of photographic characteristics. At the same time, samples are sent to the Film Testing Department where they are exposed and developed as a check on cleanliness and photographic quality. If all of these tests indicate that the coated roll is up to standard, it is released for slitting.
Because high speed panchromatic films can only be handled in total darkness, it is necessary to make routine tests according to a special procedure in order to locate and discard any portion of the production which shows irregularities in coating, but positive film, which can be handled under red light, is examined by trained inspectors as it runs through the slitting machines, and it is indeed seldom that any possib'e irregularity escapes their keen observation.
Perforation of each roll of 35 mm. film is the next operation, and one that requires great precision. For this reason the perforating machines are under the supervision of skilled mechanics, and samples of film from each perforator are run in a special precision projector which shows the perforations in greatly enlarged form on the screen. Any possible unsteadiness is thus instantly detected and the perforator is repaired and tested before further use. At the same time, strips from the ends of rolls of perforated film are developed, and additional samples of film from each perforator are optically measured on a stereo comparator, an instrument accurate to 1/25000 of an inch, to insure standard pitch and alignment of perforations. As a further precaution, the perforators used for negative materials are checked at frequent intervals by measuring perforated film with the stereo comparator, thus insuring precision and cleanliness in the cutting of individual perforations.
When 35 mm. film has passed all tests for accuracy of width, thickness, edge printing, perforations and other physical characteristics which are measured during production, samples of the film are sent to the Testing Department for sensitometric tests, and special tests to determine resistance to age and other factors which adversely affect unexposed materials during storage. In
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