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Old April 5, 2013, 07:37 AM   #72
Senior Member
Join Date: October 8, 2006
Location: Northern Michigan
Posts: 2,772
Using Plum Brown...
Does the surface to be browned need to be completely free of previous bluing?
I've never applied Plum Brown over blued metal, or 'partially' blued metal. However, I have used it to cover worn rust browned surfaces and it worked just fine, so I suspect the answer is no. Both Plum Brown and Laurel Mountain finishes are opaque, not translucent, so repeated applications will cover surface coloration inconsistencies. The color just gets deeper and more uniform, a lot like painting with a heavy glaze.

Does the process produce a markedly different appearance when applied to case hardened parts?
I'd say 'noticeably' different with light application, much less so the more coats you add. Plum Brown, like Laurel Mountain, works by rusting the surface of the metal. A chemically 'color case hardened' surface (if that's what you meant) will resist that process more than an untreated steel, so it will take more work. If you meant a truly case hardened surface I don't really know for sure what it will do, but I suspect it will be closer to untreated steel than the chemically 'hardened' surface. I've seen work that was very dark brown, almost black, and I believe it started as a bone charcoal hardened surface that was then treated with Plum Brown. In the end it's speculation as I really have no personal experience with it.
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