M1905 Bayo Strange Patina From ???

[Milsurf]

NR from the CMP forum, maybe the experts are lurking here? I recently obtained a 16 inch bayo (stamped SA, flaming bomb, 1908, US and 267649) off Fleabay. It cost only a C-note and obviously had some rusting, and so I wasn't expecting a stellar example. While indeed it isn't, what arrived is markedly better than what I was anticipating. It has some deeper rust and pitting along the unsharpened edge and at the point, apparently due to condensation or other prolonged water contact. But most of the blade is fairly smooth and clean, seemingly with a patina due to air, not liquid water, oxidation. Most of the metal shows a black, non-pitted surface surrounding a myriad of silver dots. See photos below:





Note that the pics appear to show substantial roughness, but on the contrary the surface is very smooth and the dark areas shown are not depressed (pitted). In the small areas of deeper rusting and subsequent pitting (see the patch at the upper right of the top photo), the surface is all black with no silvery points.

Are there any metallurgists or other knowledgeable types here who might explain this surface? I'm guessing that this blade has had a (unique?) oxidation history that now shows the metallic grain structure at the surface, the silvery grains perhaps containing a bit more chromium and/or nickel than the dark ones. I welcome any informed confirmations or denials!

Information

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[browningautorifle]

This isn't magic. Not really unique either... This was probably stored on the beam of the barn or garage for 30 years and took a heavy coat of red dry rust. It was scrubbed off with dry steel wool and sold. The deeper stuff is just pitting, it can all be resurrected, I've done them. It won't look too bad after either.

[Milsurf]

Thanks. I don't think I'll try to "clean up" this bayo, the surface effect it now exhibits is somewhat remarkable, IMO. I have never seen anything quite like it in over thirty years of collecting firearms and Japanese swords. I still tend to think that the mottling is indicative of the (rather fine) grain structure of the metal in the blade.