Alphonse Louis Poitevin (11 February 1800 – 17 September 1877) – a French chemist, was one of the most important inventors of the early days of photography and indeed the digital printing processes in use today. His main inventions include photographic and photomechanical processes now known as carbon printing and collotype printing.
The carbon process, initially a black-and-white process using lampblack (carbon black), was invented by Poitevin in 1855. The process was later adapted to color, through the use of pigments, by Louis Arthur Ducos du Hauron in 1868. Carbon printing remained commercially popular through the first half of the 20th century. It was replaced over time by the dye-transfer process, chromogenic, dye-bleach (or dye destruction, i.e., Cibachrome) and, now, digital printing processes. The efficiencies gained through these more modern automated processes relegated carbon printing to the commercial backwaters in the latter half of the 20th century. It is now only found in the darkrooms of the rare enthusiast and a few exotic labs.
The innovations of the early photographers are important to the screenprinting process as are precursors to the photographic emulsions in use today. The first photographic stencils were made with a gum arabic/dichromate mixture.
Gum bichromate is a deceptively simple process which involves just a single light sensitive chemical, is developed in water, and can be printed on a variety of papers and other surfaces used in the photography field.
No one person can be credited with having discovered the gum process. Rather it was the continual investigation of several pioneers who evolved the process into its current form. Today gum printing continues to evolve as each practitioner brings their own interests and sensibilities to the process.
1826 – Fox Talbot contributes findings in a paper on “Some Experiments on Color Flame” to the Edinburgh Journal of Science.
1827 – Fox Talbot contributes a paper on “Monochromatic Light” to the Quarterly Journal of Science and to the Philosophical Magazine a number of papers on chemical subjects, including one on “Chemical Changes of Colour.”
1835 – Fox Talbot produces a print “Latticed Window in Lacock Abbey” in 1835 was made from what is considered the oldest photographic negative in existence.
1838 – Mongo Ponton is credited with discovering the light sensitivity of dichromate.
1835 – Alphonse Louis Poitevin added pigment to the gum arabic/dichromate mixture.
1839 – Louis Daguerre exhibited his pictures taken by the sun.
1841 – Fox Talbot announced his discovery of the calotype, or talbotype, process for which he received a patent and licensed Henry Collen (1798-1879), the miniature painter as the first professional calotypist. Talbot’s negative/positive process eventually succeeded as the basis for almost all 19th and 20th century photography.
1842 – Fox Talbot receives the Rumford Medal of the Royal Society for his photographic discoveries, which were later detailed in his The Pencil of Nature (1844).
1851 – Frederick Scott Archer publicized the collodion process.
1861 – Alphonse Louis Poitevin, found that ferro-gallate in gum is light sensitive. Light turns this to an insoluble permanent blue. A coating of this chemical on a paper or other base may be used to reproduce an image from a translucent document. This was to become the basis first blueprint.
1890 – Van Hubl introduced the practice of re-sensitising the image and then reprinting it in registration under the same negative. This adaptation to the process was probably one of the most significant, for it allowed the gum printer to build up tone and texture through repeated printings. Single printings in gum tend to be rather flat with poor detail and tonal separation. But the multiple gum print allows the print-maker to build up considerable tonal range and detail.
1890 – Alphonse Louis Poitevin’s process was revived by those who were attracted by the ease with which the wet emulsion could be manipulated.
Gum Print Basics
The gum print works on the principle that an organic colloid (in this case gum Arabic) when combined with a dichromate becomes light sensitive. Exposure of this dichromated colloid to light causes the organic colloid (gum arabic) to harden in proportion to the light striking it, much like the screenprinting emulsions of today. Adding watercolor pigment to the gum provides the color. Development is achieved by floating the exposed print in water for 30 minutes or more. The unhardened gum is washed away, leaving the hardened, exposed gum to form the image on the paper.
The gum print, unlike most traditional photographic prints, can be physically manipulated to a considerable extent. During development, when the print is wet and fragile, details can be rubbed out with the use of a brush or water jet. Images can be re-sensitised and re-exposed several times, either to deepen tone or to achieve definite color shifts. Tone, texture and color can all be altered and manipulated.
Most photographic processes are essentially the product of chemical interaction, but gum printing is a balance between chemical and physical interaction.
Outline of the procedure of gum printing
Creating a gum (or gum bichromate) print involves applying an emulsion of watercolor and gum arabic, combined with an ammonium or potassium dichromate sensitiser onto sized paper. After drying, the emulsion is exposed by contact with a UV light source. Available sources include; sunlamps, UV BL fluorescent tubes, Mercury Vapor lamps, or sunlight. Development of the image is achieved by floating the print on water. The water penetrates the gum and permits the un-hardened gum to dissolve. Development takes around 30 minutes. After one layer has dried the paper may be re-coated and exposed again. Anything from three to sixteen printings is possible, depending on the extent of staining of the paper by pigment. Paper choice, intensity of pigment and other factors all affect the number of coats possible.