Some etches undercut the masking layer and form cavities with sloping sidewalls. It rapidly etches the surface of semiconductors such as silicon. This gas etches metal oxides by formation of a volatile BOCl compounds. Modern processes greatly prefer anisotropic etches, because they produce sharp, well-controlled features. Hydrogen is essential because it selectively etches off non-diamond carbon. The etches cores are typically punched to add lamination tooling. It includes transfers, brass etches, most nameplates and cast white metal parts. This etches the work-piece surface and removes any scale. While carving pumpkins, Bart takes a knife and etches a smile into Homer's pants. Then acid etches away the material not protected. It includes transfers, brass etches and cast white metal parts. Souvenirs one can buy in Chile include wines, copper etches, wood carvings, and textiles. In 2011, he starred as Mark Etches in the British supernatural drama "The Fades". Artist Rolf Weijburg produced various etches on Saint Helena, picturing various of these endemic birds. A laser then etches the chip's name and numbers on the package.