Hi - Ran across this youtube video (http://www.youtube.com/watch?v=R9oaSR2yWyQ) and at 1:31 it shows a black stick being used to blacken a machine engraving on a ring. My assumption is since it's being used on a ring it's pretty durable, and it sure is dark. Any ideas or thoughts? If I'm breaking a rule by posting a link I apologize in advance. Bob