A lumen print is an image made by laying an object, often a flower, on a sheet of black and white photo paper that has never been exposed, then putting it all in the sun. No developer: light alone brings out a coloured, detailed image, in tones ranging from pink to purple, or towards brown.
This image is fleeting. You scan it straight away, or fix it to keep it, knowing that the fixer changes its colours.
Lumen print or developed print: what is the difference
Lumen prints, photograms and cyanotypes are all made without a camera, but they do not mean the same thing.
The photogram is a principle: objects laid on a sensitive surface, whatever it is, leave their silhouette on it. On photo paper, the sheet is then developed in developer and fixed.
The lumen print starts from the same darkroom paper, but leaves it in the sun for a long time. As in solargraphy, the image then forms directly, through the darkening of the sensitive surface, with no developer.
Cyanotype, finally, uses no silver but two iron salts, which are spread on the paper. It gives Prussian blue and is developed in water.
| Process | What you need | What you get |
|---|---|---|
| Lumen print | Black and white photo paper and sun, no developer | Tones from pink to purple, browner in overcast weather |
| Developed photogram | Black and white photo paper, a few seconds under a lamp, developer then fixer | Black and white |
| Cyanotype | Paper coated with iron salts, sun or UV lamp, rinsing in water | Prussian blue |
Solargraphy relies on the same direct darkening, with no bath. But there, the paper stays for months in a pinhole camera pointed at the sky, instead of receiving objects by contact.
Same fern, three processes: the lumen print takes on colour in the sun with no bath, the photogram goes through developer, the cyanotype is rinsed in water.
Why silver takes on pink and purple tones
Today's black and white photo paper is made to be developed. A brief exposure forms a latent, invisible image on it, which the developer brings out in black.
The lumen print does without developer, like the printing-out papers of the 19th century. In these papers, light alone reduces the silver salts to metallic silver. It takes a lot of light: up to 100,000 times more than with a developing-out paper, according to James Reilly. Hence the sun, and the length of the exposure.
The silver formed this way remains as tiny particles, too small to absorb all the light and look black. They absorb only part of it, which produces these warm tones. The layer that holds the silver matters too: two different binders do not give the same colour.
The paper, the sky and the plants all vary the result. The Florida Museum of Photographic Arts cites the plants, humidity, temperature, the duration and intensity of the sun, and the type of paper.
In a project carried out at the University of Iowa, a student obtained fine detail and several colours on RC paper, which has a plastic-coated base. On fibre-based paper, she got only a white silhouette. Sunny days gave brighter colours, overcast days browner tones.
Without developer, the silver formed in the sun gives these pinks and purples; the leaf stays pale.
Analogue photo paper and the other materials
- Black and white photo paper that has never been exposed: traditional darkroom printing paper, the same photographic paper you load into a pinhole camera.
- Plants: leaves, flowers, grasses, and any organic material you want to try.
- A clean sheet of glass, or a frame, to press the objects against the sheet.
- A scanner or a phone to keep the image, and fixer if you want to preserve the original.
The Sténoflex mini-lab contains ten sheets of photographic paper, a developer, a fixer and a red safelight film. This paper is suitable for lumen printing.
Open the packet of paper under red light, and close it again straight away: one second of daylight is enough to fog the whole stack.
Exposing the photo paper, without developer
- Under red light, take out a sheet and close the packet.
- Place the sheet sensitive side up, arrange the plants, then cover everything with a clean sheet of glass.
- Take the whole thing out into full sun. Unlike a developed print, the image appears during the exposure: you can see it coming.
- Leave it to expose for a long time, judging by the tone of the background rather than by the clock.
- Bring the sheet in and remove the plants. Where a plant let a little light through, its silhouette keeps shades and veins.
- Scan straight away, then fix if you want to keep the original.
No single time works for every paper or every sky: the duration and the weather also decide the tone. To find your bearings, make a test sheet, covered with a piece of card that you remove in stages, and note what each duration gives.
Flat plants with clear outlines give the most readable silhouettes, as with any photogram. A thick plant lets light slip under its edges, and its outline softens.
In the sun, the image comes during the exposure: you judge by the tone of the background rather than by the clock.
Fixing the print or scanning it
The Museum of English Rural Life, at the University of Reading, presents the lumen print as a fleeting image, captured digitally to keep the result. Until it is fixed, the paper does indeed remain sensitive: the fixer is there precisely to dissolve the silver salts that are still sensitive.
So scan first, without delay, on a flatbed scanner or with a phone.
Then fix, if you want to keep the original: once fixed and thoroughly rinsed, the sheet is no longer affected by light.
But the fixer changes the image: it lightens it and shifts it towards reddish or yellowish browns. As it dries, it darkens again and takes on a cooler tone. So you only see the final result after fixing.
Photographers in the 19th century already knew this problem with their printing-out papers. To correct the colour, they toned the image before fixing it, often in a gold bath, which pushed it towards brown, purple or black.
| Scan without fixing | Fix | |
|---|---|---|
| Colours | Those straight out of the sun, on the file | Browner, then cooler as it dries |
| Original | Keeps deteriorating in the light | No longer affected by light |
Fixer is handled with gloves and tongs, in a well-ventilated room. Once used, it does not go down the sink: it is kept in a closed bottle and taken to a household waste recycling centre, as the precautions for photo chemicals explain.
Finally, once the image is scanned, you can either keep it as it is, with pale silhouettes on a coloured background, or invert it on the computer, as you would a solargraph.
Frequently asked questions about lumen printing
Do you need a darkroom for a lumen print?
No. You only open the packet of paper under red light, long enough to take out a sheet; everything else happens in the sun.
Can you make a lumen print in overcast weather?
Yes, but the result changes: overcast days give browner tones, sunny days brighter colours.
What happens to a lumen print that is not fixed?
It remains sensitive to light and keeps deteriorating. Scan it first, then store it away from light if you want to look at it for a while longer.
Can you make several copies of a lumen print?
No: the Florida Museum of Photographic Arts describes them as one-of-a-kind photograms. To share the image, you keep the scanned file.
Éric Marais — Photographer, author of two books on pinhole photography (published by Pearson) and creator of the Sténoflex. He has run introductory workshops in alternative photography, from pinhole to cyanotype, from the very beginning.