Sorry, no help as to what it is, but nail polish remover is the best way to get rid of it. Evidently oil will remove a bit of patina.
According to fine-tools.com the "Professional Stones" are replacement for the "Chosera" line with the main difference being that the
I thought the Chosera and Pro were one in the same. I thought the pro is just the new name with new packaging.
That looks really nice. What's the steel and, if you don't mind me asking, where did you get it?