The Backyard Scientist (who you may remember pouring molten aluminum into a watermelon) has a very cool how-to for burning Lichtenberg fractal patterns into pieces of plywood using electricity. Not only is the process mesmerizing (as you can see above), but the resulting patterns are beautiful.
Two microwave oven transformers in parallel provide the 2,000V applied to opposite corners of the 5mm plywood. A mixture of baking soda and water spread across the wood’s surface allows for better conductivity. Interestingly, the patterns flow better going with the wood grain.
This project is potentially very dangerous, so don’t try this without doing proper research and taking the proper safety precautions.
Check out the instructions or watch the video below.