Carbon Transfer Print: Classical Photography Technique: Pigment Gelatin Transfer and Notes on Permanently Fade-Resistant Prints

1. The jewel in the crown of classical printing: the eternal charm of charcoal printing

Among all classical techniques based on silver salt or iron salt, Carbon Transfer Printing is recognized as the technique with the deepest image quality, richest layers, and longest shelf life:

1. Chemical Eternity of Pure Mineral Carbon Pigments:

• The metallic silver particles of traditional silver salt photographic paper will oxidize and turn yellow due to sulfide in the air;
• The carbon printing method completely abandons metallic silver and uses extremely inert pure mineral carbon black (Lamp Black/Bone Black) as the color pigment;
• Carbon element has unshakable chemical stability under normal temperature and pressure, is resistant to strong acids and alkalis, and is resistant to ultraviolet exposure. Its storage life can theoretically last for thousands of years without fading.

2. Physical relief effect visible to the naked eye:

• The dark part of carbon printing paper contains a large amount of cross-linked and solidified gelatin and toner, with obvious physical raised thickness;
• Under side light observation, the shadows are deep and protruding, and the white paper base is exposed and sinks smoothly in the highlights, creating a breathtaking three-dimensional relief texture and a gorgeous gloss like an oil painting.

2. Preparation of carbon printing core solution and photosensitive tissue paper (Carbon Tissue)

1. Carbon gelatin photosensitive tissue fluid formula:

• Distilled water: 800ml
• High bloom (Bloom 250+) food grade pure pig skin/cow skin gelatin: 100g
• Pure carbon black pigment paste (water-based dispersion carbon black): 15g - 20g
• Glycerin (plasticizer to prevent dryness and cracking): 15ml
• Sugar (sucrose, auxiliary hydration and dissolution): 20g

2. Coating and Sensitizing:

• Completely hydrate the gelatin in a water bath at 45°C and filter out air bubbles. Use a spatula or mechanical coater to evenly coat the black glue solution on the polyester film (Melinex/Yupo paper). Cool to gel and then dry;
• Dichromate sensitization: Soak the dry tissue paper in 2% to 3% potassium dichromate (Potassium Dichromate) or ammonium dichromate aqueous solution for 3 minutes under safe yellow light;
• The sensitized tissue paper should be placed flat in a light-proof low-temperature drying oven to air-dry. It must be used within 24 to 48 hours, otherwise it will self-darkening, harden, and be scrapped.

3. Combined contact exposure and cold water transfer

1. Contrast requirements for large format negatives:

• The carbon printing method has extremely high tonal latitude and requires large-format negatives (or high-precision inkjet digital intermediate negatives) with high contrast and high density (D-max reaches 1.8 to 2.2);

2. High Energy UV Exposure:

• Place the sensitized tissue paper and negative film tightly into the vacuum printing frame;
• Use UV printing lamp (365nm-405nm wavelength) for long-term high-energy exposure (about 3 to 8 minutes);
• Physical mechanism of hardening: Hexavalent chromium ions excited by ultraviolet rays are reduced to trivalent chromium, causing irreversible covalent cross-linking and hardening of the surrounding gelatin polypeptide chains; the more fully photosensitive the place, the deeper the hardened layer.

3. Cold water combination and initial fitting:

• Immerse the exposed photosensitive tissue paper together with the final carrier paper that has been pre-hardened with gelatin coating (such as Arches watercolor paper) in cold water at 18°C;
• After the two pieces of paper have absorbed water, softened and unfolded, the glue faces are tightly attached to each other, then take them out and place them on a glass plate;
• Use a rubber scraper to completely scrape out the excess moisture and tiny air bubbles in the interlayer, then cover it with a heavy object and let it sit for 20 minutes to establish molecular adsorption.

4. Practical operation of warm water development, peeling and secondary transfer

1. Warm water development (40℃-43℃):

• Immerse the combined "sandwich" layers in 42°C constant temperature hot water;
• Wait for 2 to 3 minutes, and the soluble excess gelatin that has not been hardened by ultraviolet rays will begin to melt and overflow, oozing out like ink;
  -Pinch a corner of the original tissue paper and peel it off as a whole very gently under water! At this time, most of the unhardened ink glue is discarded with the original film, and the hardened high-density carbon glue remains firmly on the final carrier paper.

2. Warm water rinsing and relief (Washing & Clearing):

• Hold the edge of the carrier paper with both hands and gently shake it in warm water. The remaining gelatin that has not been melted by photosensitivity is completely dissolved and washed;
• The photo gradually appears under the water, from pure white highlights to thick relief shadows blooming clearly;
• Then move the photo to a cold water tank to re-solidify the gelatin, and finally soak it in a 5% sodium metabisulfite solution to remove the remaining yellow chromium salts, then rinse and dry it thoroughly.

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