I only recently learned about lumen prints after various contacts on flickr and elsewhere posted scans labelled as “lumen prints”, which at the time didn’t mean much to me – at first I thought it was some obscure process requiring a special kit of chemicals, like cyanotypes. However, a bit more reading and it all turns out to be much simpler.
We’re familiar with the idea that exposing traditional photographic media to light causes a change in the media. Under normal conditions the amount of light is so slight that the change is invisible, and a visible image can be formed only by developing the film or paper in a chemical bath. However under intense enough light – especially ultraviolet – the change in the media can become visible. Rather than a few molecules in the silver halide grains in the emulsion turning to free silver and forming an invisible image, if you expose to enough light the grains turn entirely to silver and you get a visible image without requiring development.
The easiest way to do this is to use ordinary photographic paper and put it in direct sunlight. Obviously a blank sheet of paper isn’t going to make a very interesting image, so you can place objects on the paper and record their shadows. For my first try at these I used plant cuttings from around the garden, placing them onto sheets of some very old, expired Agfa photo paper in an old photo frame to hold them steady in the sun for a few hours. What’s interesting about these compared to the type of photogram I’ve made before in a darkroom is that whereas developed photograms tend to be very black or white, the lumen prints come out with a variety of warm brown tones and even unexpected colour such as pinks and purples.
Once they’ve sat in the sun for a few hours, the only processing required is to put them in print fixer for a few minutes. It may be advisable to give them a soak in water beforehand to loosen any bits of vegetation still sticking to the surface. In the fixer the tones are somewhat bleached so the overall effect is a lot more subtle than it appears when you first get it out of the sun. I’m quite pleased with these first experiments; they capture a lot more fine detail than I was expecting at first and I find the ghostly, x-ray like finish quite appealing. In future, I may try scanning before fixing to capture that initial image and do a comparison.