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528 History of Three-Color Photography
For use 6 ccs. should be added to 60 ccs. water and 2 ccs. of rodinal added. If the solution turns thick and muddy before the necessary intensification is obtained, it should be thrown away and fresh applied.
Varnishing the Plate. — In order to protect the somewhat delicate film, it is advisable to varnish it, and the makers of the plate recommended :
Gum dammar 200 g.
Benzol 1000 ccs.
The plate must be thoroughly dry, and it is preferable to warm it before applying the varnish.
E. Valenta100 recommended a 10 per cent solution of dammar in carbon tetrachloride or :
Gum dammar 20 g.
Manilla copal, powdered 50 g.
Carbon tetrachloride 1000 ccs.
As soon as the resins are dissolved, the mixture should be heated to the boiling point, and then filtered while hot. G. Le Roy101 suggested :
Gum dammar 66 g.
Gum mastic 66 g.
Carbon tetrachloride 1000 ccs.
G. E. Brown and Welborne Piper102 recommended celluloid dissolved in amyl acetate ; but E. Konig103 strongly advised against this or any varnish containing nitrocellulose, as the latter under the action of light gives off nitrous fumes, which would be apt to attack the dyes of the screen elements.
Failures. — The following is a list of possible failures and their remedies, details of which have been collected from various sources.
Frilling. — The early batches of the Autochrome plate were very prone to this trouble, due to some peculiarity in their manufacture ; but the later ones show but little signs of this defect. The most satisfactory remedies seem to have been the reduction of the alcohol in the developer, varnishing or waxing the edges of the plate, and after reversal, binding the edges with a strip of adhesive plaster.
Black Spots. — These are unavoidable faults in the manufacture, and can be removed by touching them wdth the acid reversing solution, dipping into water and fixing. Or they may be touched with a very fine camel's hair brush, or the pointed end of a match with :
Potassium iodide 1 g.
Iodine 1 g.
Water 50 ccs.
And then fixing. They were apparently metallic silver, which was by this treatment, converted into silver iodide, which dissolved in the hypo.
Dark Brown or Blackish Patches. — These must not be confounded with the previous defect. They are much larger, more diffuse as to their edges, and more frequently make their appearance on those parts of the picture that should be colorless. They may be due to (a) incomplete