....Before re-browning any figured barrel it is essential that the old brown be effectually removed. The barrel must be well polished again before re-browning, if that fine sheen so much desired is required; otherwise, simply rubbing off the brown with emery cloth, with fine emery in water, or by sponging the barrel with strong vinegar, will answer the purpose.
I think this comment may be significant. It looks like for differences in color to appear, the barrel surface needs to start off uniform. It's been mentioned that some of the barrel finishes don't just stain or color a component, but physically alter the surface roughness, for lack of a better term, differently for the different components.
While it may not be applicable at all, if you'd like to look at knife making examples, maybe look at wrought iron san mai. It's just a forge welded external layer of wrought laminated on the sides of a blade. Anyway, the wrought, not the modern carbon steel core/cutting edge, would likely be of the era from around when some of these barrels were made. On many of them, you can see how differently the wrought iron finishes based on differing grit of finish from rough forged to high polish on the same piece.
I think a meaningful difference could be that the stringy look of wrought iron that can show, might be significantly reduced by the heavy drawing process that it looks like the barrel makers did on most every step of the way. Always interesting stuff Doc Drew, and I appreciate your historical research.
