Varnish has several purposes in instrument making: It forms a protective layer, it helps optimize the sound properties of the instrument, and it contributes to the appearance of the instrument. As a rule, multiple coats of varnish are applied over a ground coat that seals the pores of the wood. Oil-based varnish is commonly used for high-quality instruments. As the layers of varnish are subject to permanent wear, they are usually protected by a clear protective coating. The varnish properties including its color and texture are typical stylistic elements that may be used as criteria to attribute an instrument to a maker.