Sealants are applied to metal leaf to protect its appearance. While pure gold leaf does not need to be sealed a sealant is usually applied to help insure that the leaf does not wear away over time. Composition and other leafs must be sealed to prevent oxidation and tarnishing. Often times it is desirable to tone down the leaf by applying a water-based glaze. If this effect is desired, it is important to seal the leaf before applying the glaze. Common sealants include urethanes and shellac, but there are some excellent water-based sealants available.