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Three-Color Transparencies and Lantern Slides 451
even pull. These tacky sheets may be used repeatedly, four or five dozen times without harm.
To prepare a suitable sensitive film the following may be used :
Carpenter's fine glue 55 g.
Water 1000 ccs.
This glue is the finest and palest glue that can be obtained and it should be allowed to soak in the water for 12 hours. The correct method of working is to weigh the jar or beaker empty, then weigh in the glue and measure the water. At the expiration of the soaking pour off the water and add enough water to make the weight 660 g. and add :
Gelatin 55 g.
Allow to soak for 30 minutes, then raise to 50° C, stir till dissolved and add:
Alcohol 40 ccs.
To this should be added some emulsion of silver bromide, and this can be made as follows:
Gelatin 10 g.
Potassium bromide 6 g.
Water 100 ccs.
Allow the gelatin to soak for 10 minutes, melt at 50° C., and add slowly with constant stirring:
Silver nitrate 5 g.
Water 50 ccs.
This can be made by artificial light, as the silver salt merely plays the part of an inert pigment, and prevents too high a relief ; its light-sensitiveness is not used.
Keep the emulsion at the above temperature for about 15 minutes, then pour out to set in a flat dish, and leave all night, preferably on ice. Next morning score the emulsion with a silver fork lengthwise and then across, so as to break it up into little lumps. Place these in a clean cloth and suspend in water. The water should be changed six times in half an hour, giving the bag a squeeze after each change. Leave to drain for an hour and melt at the above temperature and add 75 ccs. alcohol. This should then be mixed with the warm gelatin-glue mixture and should give about 1000 ccs. of a milky emulsion. This may be sensitized by the addition of :
Ammonium dichromate 30 g.
Potassium dichromate 10 g.
And immediately coated. Or the plain emulsion, that is without the dichromate, may be used, and the plates sensitized as required. The plates coated with the sensitized emulsion will not keep more than two or three days, while the plain ones will keep indefinitely.
F. G. Tutton27 described a method of intensifying three-color transparencies and prints by subsequent bathing in dye solutions. The dyes recommended by von Hiibl were found to be the best, naphthol yellow and auramin for the yellow; erythrosin for the red and fast greenish-blue