"I take some coffee and let it splash onto a piece of paper," Stefan explains the process on his Facebook page. "After drying for about 4 to 6 hours I can draw directly onto the stain. I try to see a character or figure in it and when I find something, I draw it."
Here are some examples of his work. You can find more impressive pieces on his Instagram.
[h/t: Bored Panda]