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TINTING AND TONING MOTION PICTURE FILM 585
In developing reversal film, the film should look almost opaque when the development is finished, and the black portions of the negative should appear of almost equal density from either side of the film. The following table will be useful in timing the development:
If the first signs of image appear in: Develop for
Up to 20 seconds 5 to 8 minutes
30 seconds 10 minutes
40 seconds 12 minutes
1 minute 1 5 minutes
1J4' to 1H minutes 20 to 25 minutes
Reversion is in this case carried out chemically, by use of the following reversion bath:
Potassium Permanganate 3 0 grains
Sulphuric Acid 1 7 0 minims
Water .... 3 5 ounces
The acid should be added last in a slow stream, stirring the while. Sodium Bisulphate (380 grains) may be substituted for the acid, but is not so effective.
In reversion the negative is dissolved away and the film takes on a red color. This normally takes from seven to ten minutes, but should in any case be continued until all of the black image is dissolved. If the amateur has both orange and red lights on his darkroom lamp, the red one may be removed after the film has been five minutes in this bath.
After reversion the film is washed until it becomes a clear yellow — usually about seven minutes. The remaining operations may be carried out in white light.
The next step is bleaching, by the following formula:
Sodium Sulphite (crystals) , 150 grains
Sulphuric Acid 3 5 minims
Water 3 5 ounces
Immerse the film in this until the parts formerly densest become quite transparent. If there are found to be dark spots on the film, reversion is not complete: rinse the film thoroughly and return it to the reversion bath. Then wash, and bleach again.
The final step is darkening: this is done in a solution prepared by adding 150 grains of Sodium Hydrosulphite (NOT hyposulphite) to the bleaching bath. The film is placed in this, and the image steadily darkens until a good, brownish-black positive is produced. It is important that the Sodium Hydrosulphite be perfectly fresh: otherwise the image may not darken sufficiently, or may turn an unsatisfactory sepia tone.
After darkening, the film should be thoroughly washed in running water — at least 15 minutes — and then dried. Each of these solutions is sufficient for about 30 feet of substandard film, although the developer will last for about 90 feet. The quantities given here are those intended for use in the tanks made by the Pathex people in Europe, which hold 26 feet of film (one full Pathex charger) . They are not as yet available in America, but may be had either from MM. Pathe-Enseignement, 20 bis rue La Fayette, Paris, 9e, France, or from Pathescope, Ltd., 5 Lisle Street, London, W.C. 2, England. The solutions recommended can, of course, be made up