Metal Etching Pen

We use these pens to mark our customers saw blades, router bits, and shaper cutters names on them, when they return them for sharpening. This pen makes a permenant mark, that won't rub or wear off like ink. I'm not a chemist, but I think the etching liquid in the pen is like gun blueing. We generally wipe the writing with WD-40 oil to neutralize the etching once the writing is as dark as we want.