Int 1777, Georg Lichtenberg found that discharging high voltage on an insulating surface covered with a powder, a fractal-like image appears, sometimes known as a lightning tree. Incidentally, this is a crude form of xerography, the principle that lets copiers and laser printers operate.
[PaulGetson] had a high voltage power source from his Jacob’s ladder experiments and decide to see if he could create Lichtenberg figures. Turns out, he could.
If you have a source of high voltage, the rest of the project is pretty simple. A piece of plywood serves as the insulator and baking soda crystals cause the top layer of wood to be more conductive. Adhesive in the plywood, however, prevents the solution from soaking to the core of the board.
Another interesting trick is the use of mini cups as high voltage insulators. These are readily available and inexpensive. It is a different high voltage setup, but you can see a similar experiment on the video below.