Dykem, like you pointed out, is layout fluid for machining applications. You paint it on your steel, etch mark your work, then do your machining. It withstands heat, believe me! It's transparent, very clear color, makes a beautiful red on a light lens, and lets way more light thru than a filter does. The only concern is taking it off of a plastic lens. If you use acetone or laquer thinner it could melt the lens and permanently cloud it.