I'm trying to think of a name. When I took shop we had some stuff we'd put on metal parts to see where they needed fitting. For the life of me I can't remember the name. I think it was blue or purple too. And if you got it on your skin, it took forever to get it off.
Or, drafting ink?
It doesn't bother me, I'm just curious. The stain is part of the machines history.
Joe