Reply by rantingrich

Black pipe has a coating of what is referred to as “JAPAN BLACK” its a tar like coating. I used laquar thinner and course steel wool to scrub it off. I do this before I turn them into bar clamps. Not only does the coating act as a lubricant and lets the clamp slide, it also get on your project.

I know this won’t do anything for worn out old pipe but just saying

-- Rich