Anthotype: Photographs from Plant Pigments
Summary
Sir John Herschel1’s anthotype (1842) is the gentlest photographic process there is: a plant pigment coated on paper, exposed under a positive for days or weeks, bleaches in the light and survives in the shade. There are no toxic salts and no fixing step — just the same pigments you met making natural indicators, plus patience. You’ll see photochemistry stripped to its essence: light breaking coloured molecules apart.
History
Herschel — who named the “positive,” “negative,” and “snapshot,” and gave Talbot the thiosulfate fixer — also noticed that many plant colours fade in sunlight and turned that into an image process. Anthotypes were always a curiosity rather than a practical medium, precisely because they can’t be fixed: the light that makes them keeps unmaking them. Anna Atkins, famous for her cyanotype botanicals, experimented with them too. Today they survive as a beautiful demonstration of pure organic photochemistry.
Hazards & preparation
About as safe as an experiment gets — the materials are food and flowers.
- Rubbing alcohol is used to extract some pigments; keep it away from flames and ventilate.
- Long sun exposures mean a sunny windowsill for days — just don’t leave it where it’ll be disturbed.
See the Safety page for general habits.
Part A — Make a Pigment Emulsion
Choose a strongly coloured, light-fugitive pigment and extract it concentrated.
| Pigment source | Colour | Speed |
|---|---|---|
| Turmeric (in rubbing alcohol) | Yellow | Fast — very light-sensitive |
| Beet juice | Red-pink | Medium |
| Red cabbage | Purple | Medium (also pH-sensitive) |
| Spinach (chlorophyll, in alcohol) | Green | Slow — long exposure |
| Rose or other petals | Pink | Classic, medium |
Steps:
- Crush or blend the material with a little water or rubbing alcohol to pull out a deep, concentrated colour.
- Strain to a smooth liquid.
Part B — Coat and Dry
- Brush an even layer of the pigment onto watercolour paper.
- Dry in the dark. Repeat for a richer, more saturated coat.
Part C — Expose
- Lay a positive image or flat objects (leaves, lace, cut-paper shapes) in contact with the paper under a sheet of glass.
- Set it in direct sun. Exposure is slow — anywhere from several hours (turmeric) to weeks (chlorophyll).
- The uncovered areas gradually bleach; the shaded areas keep their colour.
The result is a soft image the same way round as your positive: pale where light reached, coloured where it was blocked.
What you should see
A ghostly monochrome image in the pigment’s own colour — a turmeric print bleaches from yellow to near-white in the highlights within a day of strong sun, while a chlorophyll print may take a fortnight. Because there is no fixer, the image keeps fading in light: view it briefly in dim light, or scan it immediately to keep a permanent copy.
| Symptom | Likely cause | Fix |
|---|---|---|
| No visible bleaching | Pigment not light-fugitive, or too little sun | Use turmeric or beet; longer, stronger exposure |
| Whole sheet faded evenly | Positive not opaque / poor contact | Use a denser positive; clamp firmly under glass |
| Colour uneven | Streaky coat | Coat thinner, multiple dried layers |
The Science
Anthotype is photochemical bleaching: the pigment molecules absorb UV and visible photons, and the absorbed energy breaks the conjugated bond system (the chromophore) that gives the molecule its colour. Once that system is disrupted, the fragment no longer absorbs visible light, so the area turns pale. Shaded areas keep their intact pigment and stay coloured.
This is the opposite polarity to the silver and iron processes: there, light builds a dark image by reducing metal ions; here, light destroys colour. And it’s unfixable for a fundamental reason — the pigment that remains is exactly the molecule that light attacks, so there’s no way to make the survivors light-stable without changing them.
Questions to Explore
Why can’t an anthotype be fixed like a silver print? What is being preserved, and why is that a problem?
Hint / answer
The image is the surviving pigment — and that pigment is precisely what light bleaches. Any remaining colour stays vulnerable, so there’s no chemical step that removes the light-sensitivity while keeping the image.
Why is a turmeric print fast but a chlorophyll print slow? What makes a pigment “fast”?
Hint / answer
A fast pigment absorbs strongly in the sun’s spectrum and its chromophore breaks easily. Curcumin is very light-fugitive; chlorophyll is more robust and less efficiently bleached, so it needs far longer exposure.
How is this the “opposite” of a Van Dyke print? Compare what light does in each.
Hint / answer
In Van Dyke light creates dark metallic silver by reduction; in an anthotype light removes colour by breaking the pigment. One builds an image, the other erases one.
Going further
- Rank your pigments. Coat strips of several extracts and expose them together to build a light-fastness league table.
- Tie it to indicators. Red cabbage is both pH- and light-sensitive — see Natural pH Indicators for its other trick.
- In the Redox track: contrast light-driven destruction here with light-driven reduction in the cyanotype and Van Dyke prints.
Footnotes
John Herschel — English polymath (1792–1871) who invented the cyanotype photographic process in 1842.↩︎