Photochrom
From The Art and Popular Culture Encyclopedia
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Photochrom (also called the Aäc process) prints are colorized images produced from black and white photographic negatives via the direct photographic transfer of a negative on to lithographic printing plates.
History
The process was invented in the 1880s by Hans Jakob Schmid (1856-1924), an employee of the Swiss company Orell Gessner Füssli, a printing firm with a history extending back into the 16th century. Füssli founded the stock company Photochrom Zürich (later Photoglob Zürich) as the business vehicle for the commercial exploitation of the process and both Füssli and Photoglob continue to exist today. From the mid 1890s on the process was licensed by other companies including the Detroit Photographic Company in the US and the Photochrom Company of London.
The photochrom process was most popular in the 1890s, when true color photography was first being developed but was still commercially impractical.
In 1898 the US Congress passed the Private Mailing Card Act which allowed private publishers to produce postcards. These could be mailed for a penny each (the letter rate at the time was two cents). Thousands of photochrom prints, usually of cities or landscapes, were created and sold as postcards and it is in this format that photochrome reproductions became most popular. The Detroit Photographic Company reportedly produced as many as seven million photochrom prints in some years, and ten to thirty thousand different views were offered.
After World War One, which brought an end to the craze for collecting Photochrom postcards, the chief use of the process was printing posters and art reproductions, and the last Photochrom printer operated up to 1970.
Process
A litho stone was coated with a thin layer of purified bitumen dissolved in benzene. A reversed half-tone negative was then pressed against this light-sensitive coating and an exposure in daylight made (taking from 10-30 minutes in summer, to several hours in winter). The bitumen hardened and became resistant to normal solvents in proportion to the light. The coating was then washed in turpentine solutions, removing the unhardened bitumen. It was then retouched in the tonal scale of the chosen color to strengthen or soften the tones as required. Each tint needed a separate stone bearing the appropriate retouched image, and prints were usually produced by at least six, and more commonly from 10 to 15 tint stones.
