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280 Transactions of S.M.P.E., August 1927
the screen. In this connection film which has been toned has a greater tendency to show oil spots than untoned film, which is presumably a result of the matte surface produced by certain toning processes. The oil and dirt may be effectively removed from the film by immersing in a suitable oil solvent, with or without scrubbing, and then removing the excess solvent by squeegeeing and buffing. A satisfactory machine for this purpose has been described by Faulkner.^ A less satisfactory method of applying the solvent is by means of silk plush as the film is being wound on a re winder.
Various liquids have been suggested for the above purpose but the precise effect of such liquids on the film base and on the image, so far as is known to the authors, has not been investigated. Moreover, in certain cases deterioration of the film image has been definitely traced to the use of unsuitable chemicals. An investigation to determine the most suitable liquids for the above purpose therefore seemed desirable.
Requirements of a Suitable Film Cleaning Liquid
A suitable film cleaning liquid should possess the following properties :
1. It should readily dissolve fats and mineral oils;
2. It should not affect the gelatin coating or the film base, or remove the color from film with tinted base. Also it should not attack the silver image or a tinted or toned image even on prolonged contact in the presence of moisture, because when cleaning on a re winder any excess of solvent which does not evaporate is trapped between the convolutions of the film, when it can evaporate only very slowly;
It should also not decompose on exposure to light to give products which are injurious to the film;
3. The boiling point and latent heat of vaporization should be such as to permit of sufficiently rapid drying;
4. It should be non-combustible, non-toxic, and be readily available at a reasonable price.
At the outset a survey was made of all the possible commercially available non-inflammable and inflammable oil solvents, and the most promising of these were investigated as follows.
Non-inflammable Oil Solvents
" The following compounds were selected by virtue of their suitable volatility, solvent action, and price: