Carbon printing (pigment printing) is one of the techniques in alternative photography, renowned for its deep shadows and long-lasting prints. This method is popular among artists and photography enthusiasts seeking exquisite, hand-crafted, and high-quality reproductions.

The origins of carbon printing date back to the late 19th and early 20th centuries when it was initially developed by the French artist, Alphonse Poitevin. The carbon print process involves casting a gelatin-based tissue with pigment and sensitizing it with bichromate. When this mixture is exposed to ultraviolet light, a chemical reaction occurs due to the photosensitivity of the bichromate. The bichromate ions are reduced to chromium ions. This reduction is the result of the UV energy breaking the chemical bonds in the bichromate ions. The UV-illuminated areas of the mixture solidify and become insoluble in water due to the reduction of bichromate ions. The extent of hardening is directly related to the amount of UV exposure. In areas that are exposed to more UV light, the hardening is more significant. After exposure, the gelatin mixture is soaked in warm water. During this stage of development, the unexposed and therefore still soluble gelatin dissolves and washes away, leaving an embossed image. The hardened, exposed areas remain, creating the final photographic image.

Carbon printing along with the gum bichromate process, two of the best known methods, are not based on the light sensitive properties of metal salts but the ability of bichromates to harden organic compounds.

(Photography: PhD Lilyana Karadjova)

The name “carbon” derives from the use of carbon (charcoal) as the pigment, which was employed during the discovery and development of the process. It imparts the characteristic depth in the shadows of the prints, with its relative proportion in the emulsion being the main controller of the dynamic range of the final print.

Step-by-step guidance to Carbon Printing

Step 1: To create carbon prints, you will need the following materials:

• Gelatine Bloom value of 190-250
• Vinyl sheets
• Lamp Black pigment or India ink
• Distilled water
• Sodium benzoate
• Isopropyl Alcohol
• White sugar
• Gum arabic
• Sensitizer solution (such as potassium dichromate)
• Acetone
• Squeegee or foam brush
• Negative or digital image transparency
• UV light source (such as a UV exposure unit or sunlight)
• Developing tray
• Blotting paper or towels
• Final washing tray

Step 2: Making a carbon tissue

The carbon printing process requires the production of a so-called temporary support, which serves as a medium to create the final print. The temporary support is a vinyl material on which a thin layer of gelatine solution mixed with a pigment, the so-called glop, is cast and at a later stage sensitised with bichromate. After its exposure, we practically already have an image of hardened gelatine on its surface, which will only be visible to us after its transfer to the final medium – paper.

To prepare the pigmented gelatin solution, it is advisable to prepare it in one-liter quantities. This measurement facilitates easy referencing of existing formulas and ensures an ample amount of solution for producing around 10-15 tissues measuring 20 x 30 centimeters or similar sizes. Utilizing all of the solution in one session is not mandatory, as it can be stored in a fridge and used at a later date, even weeks or months down the line.

Initiate the process by pouring 700 ml of water at a temperature ranging from 18 to 20°C into a clean container with a wide opening, such as glass or plastic container. While stirring, incorporate 100 g of gelatin (in our case Bloom value of 250) into the water and allow the mixture to rest for approximately 30 minutes. Gelatin commonly found in grocery stores is suitable for this purpose.

Prepare a container fill it with warm water maintained at a temperature of approximately 45-50°C. Submerge the container containing the gelatin solution in the warm water and let it completely liquefy.

Once the gelatin solution has fully liquefied, stir in 40g of plain white sugar. This addition imparts flexibility to the dry tissue and prevents excessive brittleness. Then, incorporate 50 ml of Isopropyl Alcohol as a surfactant and 5 grams of sodium benzoate to serve as a preservative. Fill the solution with 250ml warm water 45-50°C until the total volume reaches 1 liter, and gently stir for about a minute.

Now it is time to introduce the pigment into the gelatin solution and ensure thorough mixing. Various types of pigment can be used, provided they disperse well in water. For this particular formula, we recommend using India ink or Lampblack. India ink produces a warm black color, while Lampblack yields a more neutral black tone. The exact amount of pigment required, depends on the specific pigment and the desired contrast in the tissue. As a starting point, a 4% solution is achieved by using approximately 40g of pigment per liter of glop. If you are using Lamp Black we recommend mixing 5 grams Lamp Black with 40ml gum Arabic and 40ml distilled water. Use a small container with some coins or another metal pieces and shake it energetically to achieve homogeneous mixture. Use 40 ml of this mixture as a pigment for 1 liter of gelatin to make 4% solution.

Maintain the container of the gelatin solution in the warm water at a temperature of approximately 45-50°C for at least an hour before coating. This procedure aids in eliminating most of the bubbles that may have formed during the mixing process.

Then apply it onto a suitable base, depending on your desired final print size. Although paper can be used as the tissue base, we recommend to opt for a plastic material like transparent vinyl. The base can be coated by pouring the warm gelatin directly onto a larger-sized base and spreading it using your fingers, or by utilizing a flexible magnetic frame placed over a galvanized steel plate. After coating the base, allow the tissues to dry for a few hours, considering the humidity and temperature levels in the room. For optimal outcomes, a drying time of 48 hours is recommended. And here you are, your carbon tissue is ready!

Step 3: Prepare the Sensitizer Solution

4-layers Gum Bichromate print// Photography: Vesselina Nikolaeva

Generally, this involves dissolving the potassium dichromate in distilled water to create a diluted solution. We are using 10% K₂Cr₂O₇ solution for sensitizing. We are using one part 10% K₂Cr₂O₇ solution mixed with one part distilled water and two parts acetone. A total amount of 6ml coating solution is enough to coat 20×30 cm carbon tissue.

Step 4: Coat the Carbon Tissue

In a darkroom, using safelight or low-light environment, coat the carbon tissue with the sensitizer solution using a brush.

Step 5: Dry the Coated Tissue

Hang the coated tissue in a darkroom or low-light environment to dry. It should be kept away from direct light and heat until it is fully dry. This process may take 2-3 hours.

Step 6: Prepare the Negative or Digital Transparency

Create a digital negative or use analog one of the image you wish to print. Ensure that the size matches the desired final print size.

Step 7: Contact Printing

Place the dried, sensitized carbon tissue, sensitized side up. Position the mirrored negative or digital transparency on top of the tissue, making sure the image is aligned correctly. Use clips or weights to hold the layers together and prevent movement during exposure. In our case we are using a vacuum frame to keep this “sandwich” together.

Step 8: Expose to UV Light

Expose the sandwiched layers to UV light. You can use a UV exposure unit specifically designed for alternative photography processes or natural sunlight. The exposure time will vary depending on the specific materials and desired contrast. Typically, exposures can range from a few minutes to several hours. Exposition with our UV light in our lab, takes 4.5 minutes.

Step 9: Transferring the image to the final support

To develop the exposed carbon tissue, it is necessary to transfer it onto a final support. The support used should be slightly larger than the tissue itself and in our case it is sized paper or fixed blank silver-gelatine photo paper. Once the exposure is complete, submerge the carbon tissue, along with the final support, in a tray of cool water and let them soak for approximately a minute. Underwater, bring the tissue into contact with the final or temporary support, and then carefully lift the sandwich out of the water, allowing it to drain for a few seconds.

Next, place the sandwich on a sheet of plastic and use a squeegee or a roller shaft to remove the excess water. Apply gradually increasing pressure to effectively squeeze out the water. Remove any remaining water around the edges by blotting it off, and then place the sandwich on a sheet of clean blotting paper.

Cover the sandwich with another plastic plate and apply pressure by placing a weight on top. Let it stand under pressure for approximately 20-30 minutes, allowing the excess moisture to be absorbed by the blotting paper.

Step 10: Developing the print

Proceeding to the subsequent stage, the carbon tissue enters the development process within warm water. Transfer the amalgamation of tissue and final support to a tray filled with water heated to approximately 45-50°C. After a short period, the gelatin, which is soluble in nature, will commence melting and manifest as a gradual seepage along the tissue’s edges. At this point, it is necessary to separate the tissue from the support. Begin by lifting the tissue from one corner, employing a gentle upward motion to carefully detach it from the support. Subsequently, the tissue can be discarded as it is no longer needed.

Upon reaching this stage, visual perception will reveal not an image, but a conglomeration of pigment that is in the process of melting and oozing. In order to bring clarity to the image, engage in a gentle rocking and shaking motion within the warm water, ensuring occasional lifting of the print to allow for drainage lasting a few seconds. After an approximate duration of 4-5 minutes, a significant portion of the gelatin that remains insoluble will have been rinsed away, ultimately granting you a clear and satisfactory view of the desired image.

(Photography: Nikola Dyulgyarov)

Step 11: Final Washing

Once the development process is deemed to be finished, proceed by transferring the print to a tray filled with cool water, with a temperature ranging from 15-20°C. Continue the agitation for approximately a minute, intermittently lifting the print out of the water to facilitate drainage. Subsequently, allow the print to remain in the cool water for a duration of 2-4 minutes to enable the gelatin to solidify. Finally, hang up the print to initiate the drying process.

(Photography: PhD Lilyana Karadjova)

Remember, the carbon print process requires experimentation and practice to achieve desired results. Adjustments in exposure times, development, and other factors may be necessary to refine your technique.

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