The (BROM)OIL Process was an early photographic process that was very popular with the Pictorialists during the first half of the twentieth century.
The bromoil process was based on the oil print, whose origins go back to the mid-nineteenth century. A drawback of oil prints was that the chromated gelatin was not light sensitive enough to permit an enlarger to be used, so that negatives had to be the same dimensions as the positives.
OIL prints are made on paper with a thick gelatin layer that has been sensitized with dichromate salts. Exposure using a negative for contact-print leads to hardening of the dichromated gelatin, in direct relation of the amount of light received. After exposure the print is washed in water to get rid of the chromates. The result is a faint image, it looks like a relief in the gelatine; this is called the matrix. After drying the print gets soaked in water. The non-hardened parts absorb relatively more water than the hardened parts, so after sponge-drying the print, while still moist, one can apply a stiff oil-based paint, mostly lithographic ink. The non-mixing character of oil and water results in a coloring of the exposed (means more or less hardened) parts of the print, creating a positive image. The ink application requires considerable skill, and as a result no two prints are alike.
Bromoil prints are a direct variety of this process: One starts with a normally developed print on a silver bromide paper which is then chemically bleached and hardened. The gelatin which originally had the darkest tones, is hardened the most, the highlights remain absorbent to water. This print can then be inked like the oil print.
Gum bichromate is a 19th century photographic printing process based on the light sensitivity of dichromates.
First step : making a working emulsion of three components:
* gum arabic
* ammonium or potassium dichromate
* pigment or watercolor or gouaches or combinations (!)
The emulsion is spread on a 300 grs aquarel paper and allowed to dry in the dark. A negative is put on top and exposed to a UV light source (I use UV BL fluorescent tubes; in the beginning only the sun was used). A sheet of heavy glass to ensure even, constant contact is employed. The light source will harden the dichromate in proportion to the densities of the negative. After exposure, the paper is placed in plain water baths and allowed to develop until the unhardened portions of the emulsion have dissipated.
After one layer has dried the paper may be re-coated and exposed again.
The tricolor gum print is based upon three specifique negatives, corresponding to former CMY-filters.
Each layer is subsequently on top of each other handled as explained above. First the Yellow, then the Magenta and last the Cyan layer. The result is a more or less realistic color gum print.
The name was originally applied to fine art prints created on Iris printers in a process invented in the early 1990s but has since come to mean any high quality ink-jet print created typically using professional 8-Color to 12-Color ink-jet printers.
I use some Epson 1290 (A3+) printers and an Epson 3800 (A2+) printer to produce my paper negatives for oil- and gumprinting , and also to create FineArt inkjet prints .
The 6 cartridges of the Epson 1290 are filled with pigment based ink (one set with color, one set with 6 different UltraTone B/W ink) the Epson 3800 contains 9 cartridges with UltraChrome K3 ink; the A3 printers are used to produce prints on prepared paper like Magnani Litho, Fabriano Uno, Hahnemuehle Kupferdruck and even very thin japanese ricepaper Awagami glued to sheets of aluminum.
Paper for the Epson 3800: 325 grs Hahnemuehle FineArt Baryta Inkjet paper.