Tanning Developers

some use photography to take them into the world. others take the world into photography.
I take photography away from the world. the using excuse

Dye transfer works because …

differing thickness of gelatin gives different amounts of dye to transfer from the “matrix” to the “blank.” The gelatin of the emulsion is the same thickness before it is exposed and processed, developed. After development the emulsion is “washed off” providing a relief image. Soft gelatin washes off, melts, at 90F. To maintain an image means hardening the image forming gelatin. This is done by using a “tanning developer.” Tanning being the action of hardening gelatin.

The first versions of imbibition printing, wash-off relief, used the principle of a tanning bleach such as a dichromate. Dichromate systems were not as sharp as tanning developer systems, so dichromate methods were discarded before 1950.

  • Mees and James, The Theory of The Photographic Process, 1966, p.304
  • US 2,415,666
  • US 3,293,035
  • US 3,746,544

Further notes:

R-10a needs clearing, otherwise dyes look yellow/brown when using slip-sheet assembly method. [2.20.23]

Jos-Pe process invented by G. Koppmann in 1924(?6) was the first commercial process based upon tanning developer.

Koppman patents noted

Koppmann patented using pyrocatechin without sulfite with subsequent wash-off in hot water. Variation was to develop in a non-tanning developer then the unreduced silver halide could be exposed and developed with a tanning deverlop. Upon wash-off the primary image and gelatin would be dissolved..

Further, use of a ‘dye’ to prevent over-exposure was noticed along with using matrix emulsions “poor in silver.”