A Description of the Carbon Transfer Process
for Making Photographic Prints
Carbon transfer prints differ from all other types of photographic prints because the image sits on top of the paper surface which produces a relief, or third dimension of the image. This results in very sharp edge definition plus carbon prints display a range of tonality from dark to light unobtainable in other methods of photographic printing.
The carbon transfer process was devised in the mid 1850's; it is complex and demanding. There is only one commercially available carbon transfer product -a tissue- being made currently. The craft comprises many variables, some controlled by the person doing the printing, and some beyond the printer’s control. Therefore, no two carbon prints of the same image, even printed consecutively, will be exactly alike; a carbon transfer print is truly a hand-made, one-of-a-kind object.
To begin, carbon transfer printing is a contact printing process. This requires that the negative must be the same size as the final print. Also, the light-sensitive materials used in carbon printing only react with ultraviolet light. Enlargers that project image-forming light through a negative and a glass lens onto light-sensitive paper will not work for carbon transfer printing.
We live in an age where even the ubiquitous “miniature” 35 mm cameras are giving way to digital imagery. When carbon printing was being developed, photographic film had not even been invented; photographic images were recorded on glass plates, coated with collodion and light-sensitive silver salts and the cameras tended to be quite large by today’s standards. Now we take images produced by a camera and scan a negative or a positive, or simply electronically import a digital file with an image encoded, into a computer with some image manipulating capabilities. Through a complex set of computer ware, these images can be enlarged and colored so that they attenuate ultraviolet light and are then printed on a transparent material to the same dimensions as the final print. This is how negatives for carbon transfer prints are made. There are a very few practitioners who use ultra-large format cameras and print with in-camera negatives. These cameras are typically produce negatives measuring 11x14 inches and larger. Almost all of my images were produced using film cameras from medium-format through 8x10 view cameras. The resulting negatives were scanned into a high-resolution computer file and the inherent contrast adjusted for optimum carbon transfer printing. The finished negative is printed onto a transparent plastic material and cured before printing.
The next aspect of the craft is the process of making a gelatin based tissue. Tissue is a precise mixture of gelatin, sugar, glycerol, thymol, polyglyceride and pigment. The pigment is predominately India ink, hence the source of the carbon. To this, trace amounts of color pigments may be added to shift the tonality in the final print. This mixture is poured onto sheets of non-absorbent backing material to a thickness of .030" or .75mm and allowed to dry. This dried material is called tissue. In this state the tissue is not light-sensitive. To sensitize the tissue, it is coated with a dichromate solution after it has thoroughly dried. By varying the concentration of the dichromate solution, the contrast of the final image can be controlled. The exposure of the tissue in contact with the negative is accomplished with a high-intensity ultraviolet light source. The longer the exposure, the darker the subsequent print. My exposures average about five minutes under a 1,200 Watt UV light source.
The final support of the image can be any material, generally paper, with a gelatin surface. My images are transferred to high-quality cotton or fiber based rag photographic paper after all of the silver salts and other chemistry typical to those papers have been carefully removed. The prepared paper is immersed in a slightly acidified bath and mated to the exposed tissue, gelatin surfaces touching. After a brief time they are removed to a thick piece of glass and all the water and air is removed with the use of a squeegee and a brayer. The pair is covered with another piece of glass and weighted for 20 minutes. Then the mated pair is moved to a hot-water bath and the non-absorbent backing material is gently removed and set aside. The remaining soluble gelatin dissolves in the hot water, that gelatin that was not hardened by the dichromate’s chemical reaction with the ultra-violet light, and leaves behind the hardened gelatin. For this reason, carbon transfer prints display the unique quality of having a three dimensional effect.
The print is then moved to a cold water bath with a surfactant for a few minutes and then is allowed to dry. The print is again immersed in water and subsequently placed in a clearing bath which removes any traces of dichromate which might stain the print as it ages. Again it is dried and flattened and a final thin coat of clear gelatin is applied. Once this has dried, the print is ready to sign.
A mistake or mishap anywhere in the process produces a damaged or sub-standard image, or in some cases, no image at all.
Fred A. Dusel III