Sanger-Shepherd

“In 1900 Edward Sanger-Shepherd (ca. 1869−1927), a London scientific instrument maker, started to offer complete outfits for making natural color lantern slides with a dye imbibition printing method that became known as the Sanger-Shepherd process (Fig. 4.3).⁴ The method was the first to use a relief matrix to transfer the dyes. It consisted in printing separation negatives on a special celluloid film coated with dichromated gelatin containing large quantities of silver bromide. The silver acted as a light barrier to keep the reliefs as low as possible (high relief leads to high-contrast images). Printing was done through the celluloid base. After exposure, the films or matrices were immersed in hot water, where the unhardened gelatin was washed off. They were then fixed in sodium hyposulfite and washed to eliminate the silver. The resulting clear gelatin reliefs were stained by immersion in solutions of suitable dyes (greenish blue, pink, and yellow), and the colored images were transferred by successively squeegeeing each film onto a wet receiving sheet of gelatin-coated paper (Sanger-Shepherd 1900) (Fig. 4.4). A major problem with Sanger-Shepherd dye imbibition printing was the wandering of the dyes from the receiving gelatin layer back to the matrices, which reduced the color purity and detail rendition in the final image (Rendall 1929). For this reason the method was used mostly for making color transparencies, without any transfer of the dyes, by taping or binding the three colored films in superposition or cementing them together with Canada balsam (Fig. 4.5).⁵”

(Pénichon, Sylvie (2013): Twentieth Century Colour Photographs. The Complete Guide to Processes, Identification & Preservation. London, Los Angeles: Thames & Hudson, on pp. 128–131.)