I'm 90% certain they're painted steel, which theory is borne out by the blurb on CR, here:
http://www.classicrendezvous.com/Sweden/Crescent.htm
How improper would it be to strip and repaint them?
So it really is white paint around the lugs? I guess that qualifies as a protective coating. The reason it's not obviously paint to me is that there's black discoloration on the tubes that's not covered by the paint. I'd like to get that discoloration out if possible, and the white paint is gonna hinder that.
I had a Miyata with outlines around the lugs, but it was a fade, where this are a solid line that doesn't look very professionally executed.