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Printing from Screen Plates 559
for printing screen-plates on bleach-out paper the ordinary varnish was too soft and advised that the plate be coated with rubber, then collodion, cellulose acetate or hardened gelatin. A. Goedecke"9 patented the idea of clipping a screen-plate and sensitive plate together with paper clips on every side, which would serve as registration means after the plate was developed. J. H. Stevens'10 patented an apparatus for registering positives and viewing screens, in which one plate was firmly held and the other so that it could be shifted vertically and horizontally by levers.
The Societe Anonyme la Photographie des Couleurs01 would use a screen-plate with or without a compensating filter in the camera and transfer this negative to a support coated with dichromated colloid, provided with a similar patterned screen. Parts of the elements were protected from the developer and dissolved off. The positive elements might be made of colored resins .and these fused by alcohol vapor. E. B. Wedmore6would make separate negatives and use the imbibition method for the prints, relying on the sideways diffusion of the dyes to obtain continuous tones.
A. Schwarz03 proposed to use superimposed celluloid foils and cut across the block thus made, using the lines at right angles to those of the taking screen. O. S. Dawson and C. L. Finlay64 would take a negative through a regular patterned separate screen and print on a screen-plate coated with an ordinary emulsion. The register for printing was obtained by viewing the negative in contact with the screen-plate in a weak light, printing being effected in a strong light. In registering with the negative complementary colors were seen. W. Kunz68 proposed to take three-color separation negatives, and then to print on to screen-plates by the aid of mirrors, prisms or the like.
E. Cervenka^5 printed from negatives with a geometrical screen on to dichromated gelatin, carried by an identical screen, the picture then being immersed in stannous chloride or other decolorizer which would penetrate the unhardened colloid, and the result was transferred to paper. In an alternative method a second screen was made with bleach-out dyes and printed under the original. The same inventor07 would use a linear or regular pattern screen as close as possible to a panchromatic plate and project a positive from a lined negative through a similar screen.
J. E. Thornton68 patented a method in which a transparent support was coated with plain gelatin and the patterns mechanically printed with dyes that should soak through the colloid to the back. Or dyed grains of colloid might be scattered on a tacky surface. Sensitizing with dichromate followed and after printing, development like carbon. C. Courmont09 proposed to obtain three monochrome prints and superpose. Later70 he claimed the superposition of transparent tri-color images, obtained by any process, suitably cemented. H. Bruggemann71 projected an enlarged image