Lumen print or luminogram is a simple way to make an image using the sun usually made with an artistic purpose, created by exposure of photosensitive materials to light without the intervention of an object.
It is camera-less analog technique made on silver gelatin paper.
Lumen prints have transparent and glowing appearance like photograms but a darkroom is not necessary. The prints are fixed rather than fully developed
This technique results in image that changes its colors. It depends from different kind of paper, exposure time, subjects used on the top of the paper and every result is unique.
Plants are often used in the most of the lumen prints and some flowers and plants are easier to print than others. One can also use negatives for only to get surprising results.
When experimenting with lumens there are many options like adding water, vinegar, spices, toothpaste… and the final results is always something unexpected.