Many IWC pocket watches have plain cases, but others embody artistry and reflect skills at goldsmithing and related jewelry crafts. Some cases are 18k gold while others are silver. and later cases occasionally were steel. The finer cases have complex engravings, embossing and etching. A few have Tula work or Niello, which is a classic form of decoration involving a black mixture of copper, silver and lead sulfides, which are inlaid on engraved or etched metal.