Lumen printing is an easy and relatively cheap photographic process to achieve depending on the type of photographic paper that you use). You will need a base board ( a thick piece of card or man-made wood such as MDF works well - size depends on your print size but A4 is a good start) - a piece of glass the same size as the board - some bulldog clips to hold down the work - light sensitive photographic paper (here you need to experiment as different papers give different effects) - UV light such as the sun or a UV light source - chemical fixer - water to wash the final print - a tray or two for the liquids - tongs
Plants make an excellent source material; the flatter they are and the better contact you make between the plant and the photographic paper, the more distinct the final image appears. Through experimentation I have found that wet plants or plants containing some moisture can deeply affect the colours in the final print especially if you use Ilford Multigrade FB Warmtone papers. This paper is expensive but it does give wonderful colour effects even when fixed and washed (normal Ilford Multigrade paper does intitially give off some intertesting colour ranges but as soon as it is fixed then the colours fade and the print turns one base tone of brown or grey).
You will work in normal daylight so if you do not want to fog all of your light senstive paper then take some out of the box in the dark or in a room with red safe light; if you are going to use all of your paper for lumen printing then fog the lot. I always make a point of never throwing away any accidently fogged paper or any off cuts as these can always be used for lumen printing; keep a box of old papers just for your lumen prints. Put your paper on your base board witht the emulsion side up (facing the light source). Assemble your chosen plant or plants on the paper, then apply the piece of glass so as to weigh down the plant/s and then keep in place with the bulldog clips. Take outside and expose to sunlight (if no sunlight then use a UV light source such as a UV light box if you have one). Exposure time can be anything from a few minutes to hours, days and even months; I usally leave some of mone out for the whole of the summer, rain or sunshine). You have to experiment with exposure time as much as you need to experiment with paper types; time, effort and experimentation can result in some wonderful results.