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384 CINEMATOGRAPHIC ANNUAL
The apparatus needed is a solid drum of metal or wood, painted with a dead black photographic enamel which must be resistant to the action of photographic chemicals. A skeleton-type drum, with only ribs, cannot be used for reversal processing.
Any high-contrast developer can be used. The following is a good formula:
Hydroquinone „ _ 1 ounce
Sodium Sulphite (Dry) 11 ounces
Sodium Carbonate (Dry) .... . 7 ounces
Potassium Bromide 1 ounce
Water 1 gallon
Alcohol 1 pint
The alcohol may be omitted, but permits development at a higher temperature, giving greater contrast.
Development should be slow, by dim, red light, so as to give a snappy negative with pure whites and deep blacks. Be sure to develop fully.
Wash for five minutes or more, to remove all traces of developer.
At this stage, any swelling of the film should be taken up by tightening the film on the drum. Then the film should be exposed to a diffused, white light until the white portions of the film become visibly greyed.
The next step is to destroy the negative image by immersion in:
Water 1 gallon
Potassium Bichromate 1 Yi ounces
Nitric Acid 3 ounces
The film is immersed in this bath until the negative image has entirely disappeared, and only the creamy white of the remaining, undeveloped silver bromide is visible. After this, the film must be thoroughly washed, and the final, positive image then developed in the usual manner. This may be done in the same solution in which the negative was developed, or in some softer-working solution.
After this development, the print is fixed and washed in the usual manner.
Another set of formulae, especially intended for substandard reversal emulsions, are recommended by Messrs. Pathe for use with their Pathex system.
The formula for the first development is:
Paraphenylenediamenc .... 150 grains
Sodium Sulphite (crystals) 1 ounce
Caustic Soda 150 grains
Potassium Bromide 60 grains
Phenosafranine (Solution 1:1000) 160 minims
Water 3 5 ounces
If anhydrous sulphite is used, only ]/2 ounce is needed. There are also several commercial desensitizers. such as "Desensol," etc., which can be readily substituted for the safranine solution required.
This developer must be used at temperatures between 60° and 65° F.
The developer should be filtered before use. Remember, too, that the caustic soda is bad for the eyes, so do not splash the developer.