The origins of the oil print process go back to experiments by
Alphonse Louis Poitevin with bichromated gelatin in the 1850s. To make an oil print, a piece of paper is coated with a thick gelatin layer containing dichromate salts that sensitize it to light. A
contact print is made by laying a negative over the paper and exposing it to light, which leads to hardening of the dichromated gelatin in proportion to the amount of light that reaches the paper. After exposure, the print is soaked in water and the non-hardened areas absorb more water than the hardened parts. The sponge-dried but still moist paper is then inked with an oil-based ink, which sticks preferentially to the hardened (drier) areas. The result is a positive image in the color of the ink. As with other forms of printmaking, the ink application requires considerable skill, and no two prints are identical. Multicolor oil prints are possible through local inking of the print, and it is also possible to create reverse prints by contact-printing the wet oil print to a piece of plain paper. Artists have also sometimes created variations by applying extra paint using brushes. In the later 19th century, it was possible to buy commercially prepared gelatin-coated paper. In 1907, E. J. Wall described how it should theoretically be possible to place a negative in an enlarger to produce a larger
silver bromide positive, which would then be bleached, hardened, and inked following the oil print process. ==See also==