Carbon Transfer Printing — The Most Permanent Photographic Process Ever Made

The carbon transfer print — often simply called a carbon print — is widely regarded as the most archivally permanent and tonally beautiful of all photographic printing processes. Developed by Joseph Wilson Swan in 1864 (building on earlier work by Alphonse Poitevin and others), the carbon print uses pigmented gelatin rather than metallic silver to form the image. Because the image is composed of stable, lightfast pigment (traditionally carbon black, hence the name, but any stable pigment can be used), carbon prints do not fade — they are as permanent as the paper they are printed on. The process produces images with an extraordinary tonal range, deep rich shadows, luminous highlights, and a subtle three-dimensional relief created by the varying thickness of the pigmented gelatin layer. This guide covers the history, chemistry, tissue preparation, exposure, transfer technique, multi-colour carbon (carbro), troubleshooting, and the superlative beauty of carbon printing.

Why Carbon Printing Matters

All silver-based photographic prints — from salt prints to modern gelatin silver papers — are fundamentally impermanent: the metallic silver that forms the image is vulnerable to atmospheric pollutants, oxidation, and fading. Carbon prints bypass this limitation entirely by replacing silver with pigment. The pigment is embedded in hardened gelatin, which is itself highly stable when properly processed. Well-made carbon prints from the 1860s look as fresh today as the day they were printed — over 160 years of proven permanence. This extraordinary stability made carbon printing the preferred process for archival reproductions, fine art editions, and museum collections in the 19th century. Today, carbon printing is practised by a dedicated community of fine art photographers who demand the highest possible print quality and permanence.

How the Process Works

Carbon printing uses a sheet of gelatin mixed with pigment (carbon tissue) that has been sensitised with potassium dichromate (a light-sensitive compound). When exposed to UV light through a negative, the dichromate causes the gelatin to harden (cross-link) in proportion to the amount of light received. Where the negative is clear (corresponding to shadow areas of the image), the gelatin hardens through its full thickness. Where the negative is dense (highlights), the gelatin is hardened only superficially or not at all. After exposure, the tissue is transferred face-down onto a receiving support paper, then immersed in warm water. The warm water dissolves the unhardened gelatin (the highlight areas), which washes away carrying its pigment with it, while the hardened gelatin (the shadow areas) remains on the support paper bearing its pigment permanently. The result is a positive image in pigmented gelatin on the receiving paper — a carbon print.

Preparing Carbon Tissue

Carbon tissue is a sheet of gelatin mixed with pigment on a temporary support (traditionally a thin sheet of paper). You can make tissue from scratch by dissolving photographic-grade gelatin (typ. 250 bloom) in warm water, adding dry pigment (lamp black for monochrome, or any lightfast artists' pigment for colour work), spreading the mixture on a temporary paper support, and drying flat. Alternatively, pre-made carbon tissue is available from specialist suppliers (Bostick & Sullivan, Alternatives Photography). The tissue must be uniform in thickness — uneven tissue produces uneven tone in the print. Before exposure, the dried tissue is sensitised by immersion in a 3–5% potassium dichromate solution for 2–3 minutes, then hung to dry in the dark. The sensitised tissue is light-sensitive and must be used within 24 hours for best results.

Exposure and Transfer

The sensitised tissue is placed in contact with a negative (positive-reading, emulsion to emulsion) in a vacuum frame or printing frame and exposed to UV light — sunlight, a UV fluorescent bank, or a dedicated UV exposure unit. Exposure times depend on the UV intensity, the negative density, and the tissue thickness — typically 3–15 minutes with a UV exposure unit. After exposure, the tissue is mated face-down with a pre-soaked receiving paper (gelatin-sized 140lb+ watercolour paper) by pressing the two wet surfaces together and squeegeeing out air bubbles. The sandwich is immersed in warm water (approximately 40°C). The warm water softens the unhardened gelatin, which gradually dissolves and washes away, revealing the image in hardened pigmented gelatin on the receiving paper. The temporary support peels away, leaving the carbon image on its permanent receiving paper. This transfer step is why the process is called "carbon transfer" rather than simply "carbon printing."

Single Transfer vs Double Transfer

In single transfer, the tissue is transferred directly to the final receiving paper — but because the tissue is applied face-down, the resulting image is laterally reversed (mirror image). This is acceptable for abstract or symmetrical subjects but problematic for text, architecture, and portraits. Double transfer solves this: the tissue is first transferred to a temporary intermediate support (a sheet of gelatin-coated plastic or un-sized paper), the unhardened gelatin is washed away, and then the hardened image is re-transferred from the intermediate to the final receiving paper, restoring the correct lateral orientation. Double transfer adds a step but produces correctly oriented prints and also allows the use of a wider range of receiving papers.

Tri-Colour Carbon and Assembly Printing

Full-colour carbon prints are made by preparing three separate tissues pigmented with cyan, magenta, and yellow (the subtractive colour primaries), exposing each through a colour-separated negative, and transferring all three layers in precise registration onto a single receiving paper. The layered result is a full-colour print of extraordinary richness and permanence — all three colour layers are lightfast pigment in hardened gelatin. Tri-colour carbon printing is among the most demanding photographic processes — registration of three separate transfers to within fractions of a millimetre requires precision and practice — but the results are unequalled. Some practitioners add a fourth (black) separation for enhanced shadow depth. The process was used commercially in the early 20th century (as "carbro" printing using bromide prints rather than UV exposure) and is practised today by a small number of dedicated fine art printers.

Troubleshooting

Staining in highlights: insufficient washing — use warmer water or extend the wash time. Incomplete transfer: the tissue and receiving paper did not bond properly — ensure both surfaces are thoroughly wetted and squeegee firmly. Uneven tone: tissue was not uniform in thickness — take more care during tissue preparation. Excessive contrast: tissue was over-sensitised or over-exposed — reduce dichromate concentration or exposure time. Flat, low-contrast prints: under-exposure — increase UV exposure. Gelatin frilling (lifting from the support): receiving paper was not properly sized — re-size with a gelatin solution and harden with formalin or glyoxal.