On a trip to one of my all time favorite stores, Richards Variety, I picked up this photo kit that takes me way way back to 9th grade photography class. I remember making solar prints but this kit is pretty cool and easier than back in the days of using actual darkroom paper and chemicals. My son and I picked some random foliage on the tail end of one of our runs and brought it home to experiment with.
I used a 11x14 mounting board as my cardboard surface and arranged everything inside the house and carried it out to the back patio to expose to the sun. I was trial an error but I did end up with one I absolutely love and have ordered a frame for it. You get 15 sheets of paper and a clear acrylic sheet. You provide the cardboard, sun and water.
The paper turns white fairly quickly, less than 5 minutes for sure on a bright day. This is what it looks like before you rinse it, after it is exposed.
I used a metal dish drain and a cookie drying rack to dry my prints. I have a print drying book, and recommend using that method if you happen to have one laying around from art school (way back when I shot film and developed prints in the dark room). The paper tends to curl up so having this book to absorb the water and dry the print keeps it in much nicer shape.
The end result is the opposite effect of what you saw when you removed your subject off the paper and out of the sun. Pretty sweet!