Porcelain is resistant to all acids, but is corroded by nitric acid, and etching is a method of engraving on the surface of porcelain that takes advantage of this. When gold or paint is applied to the etched surface and fired, the etched surface becomes matte and the unetched surface has a different luster, making the pattern much more effective. However, this method is best suited for porcelain, which has a dense glaze, and does not work well with soft glazes, and is more effective with hard, high-fired porcelain. This method is applied to high-end porcelain only, because it is very dangerous and difficult to perform because of the use of nitric acid and other strong acids.
