After the powder is applied to the metal, the piece is put in a special oven and the piece is "cured" or baked on. When the powder is cured on the metal it forms a protective finish that is harder than conventional paint. Powder coating has cross linked particles that provide a waterproof finish. Whereas solvent based paint can leave very small pinholes - an inroad causing future rusting. Powder coating metal signs provides better resistance to scratching, rust, wear and tear.