Most nail polish removers have acetone as a primary active ingredient. Acetone is a powerful solvent for both oil-based and latex-based paint, and can be used to remove uncured paint from a wide variety of surfaces. Some nail polish remover is composed entirely of acetone, and can be safely used to thin paint. Check the label to see what ingredients are in your nail polish remover before using it as paint thinner.
Stir the paint thoroughly.
Add no more than one ounce of nail polish remover per gallon of paint. Stir for thirty seconds.
Test the thickness of the paint by applying a long, single stroke to a test surface. Add more acetone if required, up to a maximum of twelve ounces per gallon of paint.