Dillinger tampers are made from vacuum-hardened stainless steel. The black ones are plasma coated with a diamond-like coating. It was developed for the machining and aerospace industry (think space-flight, jet engines, machine-tools). It is so hard that the hardness measurement is off the Rockwell hardness scale (the measurement scale used by engineers to decide how tough something is)!
References allow you to track sources for this article, as well as articles that were written in response to this article.