Special care and expertise are required to avoid a wide range of issues that can occur in the investment casting process, such as pitting. Pitting is a common problem, but it can be avoided. It can occur when contamination causes pits in the surface of a cast part or when a poorly designed sprue traps air and makes bubbles on the casting surface. Bubbles and voids can also be caused by overheated alloys that create gas bubbles or when under-heated molds leave bits of wax when the pattern is melted away. Other causes also exist, all of which should be proactively addressed by the foundry.