Cobalt is a hard, silver-gray metal with a lustrous appearance, found only in natural alloy form. Cobalt base metals are utilized in many different specialized investment casting alloys. When combined with other metals cobalt alloys exhibit excellent toughness and strength, as well as high heat and corrosion resistance. It has a passivating oxide film to protect it from oxidizing. In alloy form with other metals, cobalt delivers very good performance in harsh conditions and demanding applications.