Van Dyke Brown Print

A 19th-century iron-silver printing process that turns sunlight into warm sepia images on plain paper
Intermediate🕐60 min▲Moderate hazardphotographyredox

Summary

The Van Dyke process makes a photograph from two coupled redox1 reactions: ultraviolet light reduces iron(III) to iron(II), and that iron(II) then reduces silver ions to metallic silver, building a warm brown image grain by grain. It’s the same iron photochemistry as the cyanotype but with a silver twist, and it shows why almost every historical photographic process is, at heart, reduction2 driven by photons.

History

By the 1890s the light-sensitivity of iron salts was well understood, and photographers looked for cheaper alternatives to expensive platinum prints. The Van Dyke process — named for its resemblance to the brown pigment used by the painter Anthony van Dyck — uses iron to reduce silver rather than platinum, giving a rich sepia at a fraction of the cost. It belongs to the family of iron-based “alternative processes” (cyanotype, Van Dyke, kallitype, platinum/ palladium) that share one photochemical trigger.

Hazards & preparation

Warning

PPE: safety glasses and nitrile gloves; work under low light until exposure.

  • Silver nitrate stains skin (and everything else) permanent black and is toxic — handle the sensitizer with gloves and keep it off surfaces you care about.
  • UV exposure means bright sunlight; don’t stare at UV sources.
  • Disposal: silver-bearing rinse water should not go down the drain — collect it, let the silver settle or precipitate it as the chloride, and hold the solids for hazmat. See the Safety page.

Part A — Mix the Sensitizer

Make three stock solutions, then combine them just before coating (the mixed sensitizer keeps only a few weeks).

Component Amount
Ferric ammonium citrate 9 g in 33 mL water
Tartaric acid 1.5 g in 33 mL water
Silver nitrate 3.8 g in 33 mL water

Steps:

  1. Dissolve each solid in its water separately.
  2. Combine in the order above — iron first, then tartaric acid, then silver — swirling gently. Adding silver last minimises premature precipitation.
  3. Store in an amber bottle away from light.

Part B — Coat and Dry

  1. Under subdued light, brush a thin, even layer of sensitizer onto well-sized watercolour paper.
  2. Dry in the dark (a hair dryer on low speeds this up). The coated paper is now UV-sensitive — keep it in a light-tight folder until you print.

Part C — Expose and Process

  1. Place a negative (or opaque objects, for a photogram) in contact with the coated paper under glass.
  2. Expose to strong sunlight or a UV source. A faint brown image “prints out” as you watch — typically 5–20 minutes depending on the light.
  3. Wash briefly in running water (the highlights clear).
  4. Fix for about 1 minute in 10% sodium thiosulfate (“hypo”), which dissolves the unexposed silver so it can’t darken later.
  5. Wash thoroughly — 15–20 minutes of running water — and hang to dry.

What you should see

A warm brown-to-sepia image on a slightly cream paper base, darkest where the most UV struck (under the clear parts of the negative). The tone deepens and “sets” through fixing and washing. Van Dyke prints have a distinctive antique warmth that suits portraits and botanical subjects.

Symptom Likely cause Fix
Image fades or yellows after a day Under-fixed or under-washed Fix the full minute; wash 15–20 min
Weak, pale image Under-exposed or old sensitizer Longer UV exposure; mix fresh sensitizer
Muddy highlights / overall stain Too much sensitizer, or fog from light Coat thinner; keep coated paper in the dark
Brown stains on hands/bench Silver nitrate contact Gloves; the stains wear off skin in ~1–2 weeks

The Science

The image is built by two redox steps. First, UV light photoreduces iron(III) to iron(II) in the exposed areas:

\[\ce{Fe^{3+} ->[\text{UV}] Fe^{2+}}\]

The iron(II) is a strong enough reducing agent to hand an electron to silver, depositing neutral metallic silver — the brown image substance:

\[\ce{Fe^{2+} + Ag^{+} -> Fe^{3+} + Ag^0\ (\text{brown})}\]

Fixing with thiosulfate then dissolves the unexposed silver as a soluble complex so the highlights stay clear and the print becomes light-stable. This is exactly the cyanotype’s iron photoreduction — only there the iron(II) reacts with ferricyanide to make blue Prussian-blue pigment instead of reducing silver. One photochemical trigger, two different final images.

Questions to Explore

  1. Why does the image only appear where light struck? What does UV actually change in the coating?

    Hint / answer

    UV reduces Fe³⁺ to Fe²⁺ only in the exposed areas. Only that Fe²⁺ can then reduce silver to metal, so brown silver forms exactly where light reached — a faithful map of the light pattern.

  2. Why must you fix the print? What would happen if you skipped the thiosulfate?

    Hint / answer

    Unexposed silver salt is still light-sensitive; left in place it would slowly darken everywhere until the whole sheet went brown. Thiosulfate dissolves it away, locking in the image.

  3. Van Dyke and cyanotype start from the same iron photochemistry — why is one brown and one blue? What differs after the Fe²⁺ forms?

    Hint / answer

    In Van Dyke the Fe²⁺ reduces silver ions to brown metallic silver. In the cyanotype the Fe²⁺ reacts with ferricyanide to precipitate blue Prussian blue. Same trigger, different downstream reaction, different pigment.

Going further

  • Compare processes side by side. Coat two papers from the same negative — one Van Dyke, one cyanotype — and print them together.
  • Tone it. A brief gold or selenium toning bath shifts Van Dyke browns toward cooler, more archival tones.
  • In the Redox track: see the same silver reduction run without light in the Silver Mirror, and light-free image chemistry in Salted Paper Prints.

Footnotes

  1. Redox — A reaction in which electrons transfer from one species to another, coupling oxidation with reduction.↩︎

  2. Reduction — The gain of electrons by an atom, ion, or molecule; always paired with oxidation.↩︎