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Three-Color Transparencies and Lantern Slides 449
negative, exact register being, of course, obtained. This should be stained up in blue. The exposure for this will be about two and one-half times that for the first impression, as the gelatin penetrates the red picture, so that the light-sensitiveness is reduced. An increase in dichromate is not advisable, nor is an insulating medium necessary. In the same way the yellow impression is obtained. The yellow print may be made on a separate glass from a reversed transparency and will then form the cover glass. Obviously the pinatype principle may be applied to celluloid films, that is the use of the particular dyes that will stain up hardened gelatin.
L. Errera21 patented the production of lantern slides by printing with transparent inks in superposition on a flexible support, either by collotype, or the half-tone process. Gelatin, celluloid, mica or specially prepared glass might be used as support. B. Ludwig22 patented the use of color prints on flexible transparent supports for demonstration purposes, the supports being fastened together by a stud at one corner.
F. G. Tutton23 suggested the combination of chemical toning and imbibition processes for making transparencies. From the minus-blue negative a silver transparency was to be made in the usual way. After fixation and washing this was to be toned in :
Ammonium ferric oxalate 4.75 g.
Potassium ferricyanide 4.75 g.
Glacial acetic acid 5 ccs.
Water 1000 ccs.
As soon as toned through it should be rapidly washed and immersed for a short time in an acid fixing bath, so as to remove the silver ferrocyanide. After well washing it should be immersed for 1 or 2 minutes in a 1 or 2 per cent solution of hydrochloric acid, which converts the blue into a brilliant greenish-blue. Then it should be washed in repeated changes of distilled water and dried.
To produce the yellow image a positive transparency from the bluefilter negative should be printed on a film and immersed in :
A. Potassium ferricyanide 13.5 g.
Water 1000 ccs.
B. Lead nitrate 73.5 g.
Water 1000 ccs.
For use mix 9 parts A with 1 part B and add a few drops of acetic acid. As soon as the image is completely bleached through, wash until all traces of yellow stain have disappeared, then place in the following for a few seconds :
Potassium dichromate 1.1 g.
Water 1000 ccs.
Again wash till all traces of yellow stain disappear and dry. If this be varnished with one of the commercial varnishes, such as crystal varnish, it will become more transparent.
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