Van Dyke Brown classical darkroom contact printing process and sensitizer coating

1. The history and unique tonal aesthetics of Van Dyck craftsmanship

The Van Dyke Brown Process is named after the famous 17th-century Flemish court portrait painter Anthony van Dyck. It is world-famous because the developed films show the same deep, warm, retro and elegant reddish brown and chocolate brown tones as those of the master's oil paintings:

1. Iron-Silver Photochemical Reaction Mechanism:

• A cost-effective classical process between traditional cyanotype and expensive platinum printing;
• Use ferric salt (ferric ammonium citrate) to reduce to ferrous iron under ultraviolet light. The ferrous iron then acts as a strong reducing agent to reduce free silver nitrate ions ($Ag^+$) into extremely fine microscopic pure metallic silver particles (Metallic Silver Image) in situ inside the paper cotton fiber.

2. Extremely broad continuous tones:

• Compared with the high-contrast hard-toned cyanotype process, Van Dyck has an extremely broad and soft grayscale transition, which can perfectly present the delicate and moist skin texture of portraits and the rich highlight shadows in scenery.

2. Preparation formula of sensitizing solution with three major chemical components

For preparation under low light (yellow tungsten lamp darkroom environment), high-purity deionized distilled water is required:

1. 1st solution (ferric salt):

• Weigh 9.0 g of green ferric ammonium citrate, add 30ml of distilled water and dissolve completely.

2. Liquid 2 (organic acid complexing agent):

• Weigh 1.5 g Tartaric Acid crystal and dissolve it in 30ml distilled water.
• The function of tartaric acid is to maintain a strong acidic microenvironment and inhibit the spontaneous hydrolysis and reduction of unsensitized silver salts into bottom ash.

3. 3rd solution (silver salt provider):

• Weigh 3.8 g of pure silver nitrate (Silver Nitrate, $AgNO_3$) and dissolve it in 30ml of distilled water.
• Chemical Safety Warning: Nitrile rubber gloves and goggles must be worn when handling silver nitrate! Silver nitrate solution contaminated human skin will oxidize within a few hours to form dead black spots when exposed to light, which cannot be washed away for weeks.

4. **Mixing of sensitizing solution and curing in the dark:

• Mix the 1st and 2nd liquids thoroughly and stir evenly;
• Slowly add the third liquid silver nitrate slowly, and continue to stir with a glass rod during this period;
• Add distilled water to bring the total volume to 100ml.
  -Put it into a dark light-proof glass dropper bottle, leave it in a cool, dark place to avoid light and mature for 48 hours before use. The prepared mother solution can be stored stably for several months in the refrigerator to avoid light.

3. The whole process of paper selection, painting and exposure

1. Substrate Selection:

• It is also necessary to use acid-free cotton watercolor paper that does not contain calcium carbonate buffers (such as Arches Platine paper, Fabriano Artistico cotton watercolor paper).

2. Avoid light and apply evenly (Foam Brush):

• Use a straw to draw out about 2ml of sensitizing solution and drop it in a line shape on the predetermined image area of the paper;
• Use a high-density synthetic sponge brush or a Japanese brush to spread it quickly and gently horizontally and vertically, allowing the liquid to be completely absorbed into the surface of the cotton fiber of the paper;
• Place it in an absolutely dark and dark place to dry at room temperature (about 30 minutes). The dried sensitized paper will appear light lemon yellow.

3. UV Contact Printing:

• Closely adhere the photosensitive emulsion surface of the large-format black-and-white negative film (or high-contrast digital inkjet reprint negative film) to the Van Dyke paper and lock it in the vacuum exposure frame;
• Exposure to sunlight at noon for 2 to 5 minutes (or exposure to 365nm UV light box for 8~12 minutes);
• Exposure judgment: The light-receiving area shows a clear deep orange-yellow outline under strong ultraviolet light (the latent image is highly self-developing).

4. Water washing, micro-fixation and long-term storage to prevent fading

The key to the success or failure of the Van Dyke process lies in the fixing concentration. Regular concentration of black and white fixer will instantly bleach and eat up the entire brown image:

1. Primary water washing (development):

• Wash the exposed paper in micro-flow cold water for 3~5 minutes.
• The unexposed lemon yellow liquid on the paper quickly fell off, and the image instantly transformed into a clear and rich auburn;
• A few drops of very thin citric acid will completely remove residual iron salts and prevent future yellowing.

2. Extremely diluted fixing bath (2% weak sodium thiosulfate) - core lifeblood:

• Recipe: Weigh 20g of pure sodium thiosulfate crystals and add 1000ml of water to prepare 2% very weak fixing solution (It is strictly forbidden to use acidic fast fixing solution containing hardener!).
• Soak the washed photos in weak fixer, strictly soak for only 2 to 3 minutes!
• Visual texture transformation: In the fixing solution, the bright auburn instantly undergoes a violent chemical phase change, deepening and solidifying into an extremely rich and noble Chocolate Dark Brown and Cold Brown (Deep Chocolate Brown), and the non-photosensitive silver salt is safely removed by fixation.

3. Ultimate Hypowash and Gold Toning:

• Wash in running cold water for 20 minutes (hypocleaning liquid can be added to neutralize);
• Top Art Advanced: If the photo is immersed in gold chloride (Gold Protective Solution) toner for 3 minutes before fixing, the metallic gold will partially replace the metallic silver, and the image will instantly jump from brown to extremely luxurious purple-gray and gray-black, and the photo's light-proof, durable and anti-oxidation lifespan will be increased to more than hundreds of years.

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