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FILM MANUFACTURE 27
In buying film it is well to ascertain that the film purchased is fresh, a particularly important consideration in the case of high-speed emulsions and in color film. Good commercial practice dictates that film shall not be used when it is old. In the case of low-speed materials such as yellowdyed duplicating positive, this is not so important if the film has been stored properly.
In general, it is necessary to make test exposures and to gather other sensitometric data to ascertain the operating characteristics of film materials that are to be used for commercial purposes. If this procedure is followed regularly, old material is readily detected. Should it be used subsequently, its limitations are known beforehand and its unusual characteristics taken into account. If the probable quality is at all doubtful, special care should be taken in the preparation and interpretation of such test data.
Although 16-mm raw film is a complex product, it is an excellent product under good control as it is now manufactured. The control exercised in its use, however, is rarely of an order that compares with that of manufacturing control. Both exposure and processing are in need of close watching ; it is indeed rare that the results obtained in release prints even begin to approach the capabilities of the raw film. Roll-to-roll variations in the characteristics of raw film of the same emulsion lot are quite small; special pains are taken by film manufacturers in storing film materials and manufactured raw film to assure that the variation from roll to roll will be a minimum. Such storage involves keeping temperature and humidity constant; the variations permitted are minute when compared to the variations found in places where the film is subsequently handled.
When storage conditions in the interval between manufacture and use are uniform (as is the case in film manufacturers' plants) it is reasonable to expect but a small roll-to-roll variation in the same emulsion lot even when the storage period has been as long as several months ; the conditions, however, must also have been optimum. Obviously, the variation increases as the storage period becomes longer.
It is definitely unreasonable to expect two rolls of film of the same emulsion lot to show similar characteristics if one has been stored for a long period near a heated radiator or steam pipe and the other under more normal conditions. In any case, the temperature of a storage place for raw film should not exceed 70° F. The importance of reasonable care in the storage of film can hardly be overemphasized.