Carbon Print Process
International · Carbon Print 1855–1940
A photographic print made of pigment rather than silver, which means it does not fade. Carbon prints from the 1860s look today essentially as they did when made, which cannot be said of anything else from that decade.
Origin
Developed through the 1850s and made practical by Joseph Swan's patent of 1864, the carbon process answered the most urgent problem in nineteenth-century photography: albumen and salt prints were visibly fading within years, and there was serious public concern that photography had no permanence at all. Carbon was the answer, and it was used for high-end portfolio and reproduction work into the 1940s.
Technique
A tissue coated with pigmented gelatin is sensitised in potassium dichromate, which hardens the gelatin in proportion to light exposure. After exposure under a negative, the tissue is squeegeed face-down onto a final support and the original paper backing is stripped away in warm water, washing out the unhardened gelatin from the shadows and leaving a relief image in pigment. Because the image must be transferred, it ends up laterally reversed unless a second transfer is made — a fiddly, skilled, expensive procedure, which is why the process never became routine.
The palette
Whatever pigment is chosen. Carbon black is standard, but the tissue could be made with any lightfast pigment, so sepia, red chalk, blue and green versions were all commercially available, and photographers selected the pigment as a painter selects a colour. The image has physical relief — shadows are thicker than highlights — giving a subtle three-dimensional surface, and the tonal range in the deep shadows exceeds anything achievable in silver.
Legacy
Its permanence is genuinely exceptional, and it was widely used for museum and archival reproduction of paintings before colour printing was reliable. It survives as a specialist practice among a small number of printers, valued for a depth and a physical presence that no silver or inkjet process reproduces, and its descendant, photogravure, carried the same pigment principle into commercial printing.
Palette
The colours reconstructed for this artist, with the reasoning behind each.
Pigments used: Lamp black · Bone black · Umber · Green earth