If you run out of time and can’t finish your project in one day, you don’t necessarily have to go to the trouble of completely washing your paint brushes clean. If it will be several hours before you return to your project, you can keep your paint brush from hardening by wrapping the entire head of the brush, including all bristles, in plastic wrap. The wrap should be as snug as possible without distorting the natural shape of the bristles. Use a bit of tape to secure the wrap in place, and leave the brush laying flat until you return. If it will be a day or two before you can get back to painting, stick the wrapped paint brush into the freezer. You’ll need to let it return to room temperature before using it, however.