keith, if you hadn't had a chance to read it, you may want to take a peek at: doublegunshop home page > scroll down to 'constants' > best reading material ever > index entries > vol. 7 iss. 4
Ain't that a laugh, can't figure out how to do the link thing. In a nutshell, seems you're dealing with iron oxide. I wouldn't try anything too abrasive or that might chemically react with iron oxide. If there's 'patina' present, you may not be able to recover the colors for various reasons.
Sorry about that if you are already familiar with this article.
