The first non-silver photographic process, the carbon print is part of a group of techniques that use alkaline bichromates to form the image layer. In the 19th century it was the most popular pigment printing process. With excellent stability, prints can be bright or satiny and, depending on the nature of the pigments used, the process can produce images with a wide range of tones. The most popular pigment used was black or brown charcoal.
Carbon prints were patented in 1855 by
Louis-Alphonse Poitevin, who had made use
of existing research into insolubilization under
light of bichromatic colloids – gelatin in this case.
It represented an important breakthrough in the search
for stable photographic processes.
These first carbon prints, known as "direct carbon"
or "carbon without transfer", were created using
the following steps: a sheet of paper is coated with
a mix of bichromated gelatin and pigment. It is then
dried in darkness before being exposed to light in contact
with a negative. The image is obtained in warm water: areas exposed to light are hardened and become insoluble, whilst in areas that have not been exposed, the gelatin and the pigments dissolve in the water.
If Poitevin's invention offers a large amount
of stability, it does not allow the accurate reproduction of mid tones, nor the production of images with good contrast. Essentially, the thickness of the sensitized layer applied to the paper prevents light from penetrating deeply: the lower layers of the gelatin therefore remain soluble and are carried with their pigments into the water bath. Various improvements to the process were therefore made over time, including the carbon transfer print invented in 1860: in this process, the image layer
is removed from its original support before being transferred to a second support. To tackle the problem
of the image being reversed during a single transfer, photographers then developed the double transfer technique, which allowed them to reproduce the natural sense of the subject. During this same period, commercialization of pigmented paper began and the choice of pigments grew, as for example, sienna, indigo, Prussian blue and sepia.
By the end of the 19th century, high-quality non-transfer carbon prints were also available on the market, such as Artigue Charbon-Velor and Fresson Charbon-Satin.
Visual glossary of photographic techniques
© ARCP / Mairie de Paris, 2014