Seattle artist Peregrine Church uses rain as his medium. By stenciling images and words on the sidewalk in water-repellent spray, he creates Rainworks—art pieces that appear only when it's wet outside. Instead of shelling out $45 for the paint Church uses, you can follow the lead of DIYer Dan Rojas to make your own. Rojas discovered that spray antiperspirant contains a commonly used hydrophobic chemical. Clear spray paint binds it in place, creating a cheap water repellent that can last for months. "A lot of the stuff you see," Rojas says, "was made when people put two or three products together and came up with something new."