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CHAPTER 15
16-ram FILMS AND THEIR USES
The popularity of 1 6-mm cinematography and the many applications to which it has been put since its introduction have been largely due to the characteristics of certain film emulsions. Such films were introduced in 1923 and formed the foundation upon which the Industry has been built and by which it has since grown to its present state of development. The requirements which had to be satisfied before any such process could be employed by others than those directly connected with professional film production may be briefly stated as follows: -(1) The film support should be on no account of the 'nitrate base' type or have any of the inflammable characteristics of such supports. (2) The cost of the film should be reduced to a minimum. (3) Since the majority of users would only require one copy of their films it should be possible to supply this without employing the conventional negative and positive independent film lengths. (4) The operations to be carried out by the user should be very limited and, preferably, should not be more than that of exposing the film in the camera.
Acetate Film Base
The film base used to produce sensitive materials for 16-mm work is always of the 'acetate' or so called 'safety' type. Film base is made by treating cotton linters either with nitric or acetic acid. Cotton linters are the small particles of the cotton seed which are left after the bulk of the seed has been used to make cloth or thread. After washing and bleaching these linters have the appearance of very fine powder and, by treatment with acids, may be converted into nitrocellulose. Since nitrocellulose is extremely inflamable it must then be dried by chemical dehydration and, after being dissolved and made plastic, can then be rolled into sheets of transparent film base of a suitable thickness to form a support for the sensitive emulsion. The basis of standard motion picture film is therefore nitrocellulose but, by treating the cotton with very
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