Bromoil Process

Bromoil, also Bromölumdruck is as precious printing process, no pressure method in the strict sense, but a photographic positive copying process. It was invented in 1902 by Welborne Piper and commonly used from 1907.

Basis is a Bromsilberpositiv which has been exposed to uncured and therefore swelling bromide paper. After fixation and rinsing the silver image is bleached with a Chromatbleichbad, which consists of a solution of copper sulfate, potassium bromide and potassium dichromate or ammonium dichromate.

This chemical process causes partial curing ( tanning) of the gelatin layer of the paper, which thus is insoluble in water. This tanning process is proportional to the existing silver image. This gelatin relief is watered to order a color. The non-hardened areas (light image tones ) take a long, hardened image locations corresponding to less water. The water is removed from the surface of paper and then dabbed with different types of brushes or rollers an oily ink. This remains liable only to the hardened and therefore water vacancies. This creates a positive dye image. The color is determined by the choice of the oil. By transfer printing on paper creates a Bromölumdruck. This procedure can be carried out several times, producing images of an independent appeal.

This method was also used to produce before the invention of color film color photographs, very natural color scheme: By color separation with filters (blue, green, red ) were prepared 3 -fit black - and-white photographs of a subject and the Gelatinematrizen with yellow on the blue - Red coloring on the green and blue on the Rotfilteraufnahme and then printed in multiple printings of each other.