ranb, You said that you paint yours and then indicated that the paint (sometimes?) blisters. Have you ever tried using engine paint? I think it might take care of that happening. I'm not sure if it's available in any color you'd want, it might work as a base coat though. The only problem that I can see with it is how to avoid covering up the information that you've engraved. On that note, what if instead of using a hand held engraver you put the tube over a smaller piece of pipe than used a stamp to make your lettering? You could use some pitch to hold the tube in place if it must needs be. I got the ideal from working as a jeweler over the past 10+ years and how sometimes when stamping a design (stipple) or putting a Kt. mark on a piece this has worked. Thanks for helping to point WC in the right direction.
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