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wooden rack, are twisted to cut into the wood slightly. This keeps them in positions. FIG. 2
Positive type emulsions and Superior Bulk Film's Regular and Plus are found to work much better in the following formula:
Dektol stock solution 150 cc. Water 450 cc.
Sodium Sulphocyanate 1.2 grams
Developing time at 68° P., approximately 7 minutes.
In all cases the drum should be turning at about 50 revolutions per minute.
PLEXIGLASS DRUM and trough handles longer lengths than the wooden rack. The trough is rounded on the bottom with Va inch clearance when lowered into the solution. The illustration shows drum in loading position. Fig. 3
Hardening Bath
This is used as a short stop and hardening bath. In general it is not absolutely necessary if processing temperatures are maintained under 70°F. However, it is safer to use it for all films, as the least bit of reticulation on this small size image may be disastrous.
Temperatures over 70 are extremely softening to the gelatin, and a hardener is a must. Processing has been done at temperatures of 78°-80° by hardening after the 1st and 2nd developers with good results.
Three minutes in the following formula is generally sufficient:
Potassium Chrome Alum 30 grams Water 1 liter
28 % Acetic Acid 5 ccm.
Prepare immediately before using, and use only one time. It will not keep nor remain active for more than a few hours.
Bleaching
The following bath works well with ^11 films tried:
Potassium Bichromate Water
5 grams 1 liter
When dissolved add 7 ccm. of concentrated Sulphuric Acid to the above. Do not add the water to the acid. Stir constantly while adding the acid. A stock solution can be made using
10 times the amount of Bichromate and acid, and diluted 1 to 9 of water when a fresh bath is to be made up.
Three minutes in the bleach is normal. The bath can be used over several times. When the bleaching takes 5 minutes or over, throw it away. Bleaching should continue until all black silver deposit is dissolved away. If bleaching is too slow, make up a fresh bleach immediately, dispose of the old, and bleach film with the new solution for the time to clear.
A yellow light may be used during the bleach and all further processes.
Gloves should be worn if considerable processing is done, as the chromic acid in the bleach bath can cause serious burns to the cuticle and under the finger nails.
Clearing Bath
The clearing bath is to dissolve out any residual silver chromate formed by the bleach, neutralize the chromate absorbed by the gelatin, and prepare the emulsion for the second exposure.
It is prepared by dissolving 75 grams of Sodium Sulphite in 1 liter of water. This bath may be used over and over also, but throw it away if a yellow color shows up. A new batch should be made up when a new bleach solution is made.
CONTROL STRIPS make for precise results. A. Overdevelopment. B. Normal development. C. Undervelopment. These are with normal exposure. Strip D illustrates effect of overexposure and underdevelopment. FIG. 4
The emulsion should be white at the end of the clearing period. Four minutes is enough in the bath.
The second exposure is given after the film has been in the clearing bath for 2 minutes. Expose for 2 minutes • Continued on Page 558
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