This is one of those subjects
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Charcoal bluing which creates a transparent purplish blue is accepted for pre 1800. A cared for arm with Charcoal blue will eventually turn grayish the finish tends to go away through the decades.
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One thing that I think is missed in these discussions is the fact that the original barrels were wrought iron. Wrought iron has totally different properties than modern steel. Wrought iron is softer but does not rust like steel. A fresh iron barrel may have been a pleasing gray needing no finish at all.
You can see the grain in wrought iron barrles where they were pounded over a mandrell. This grain looks like it can be reproduced by draw filing across the flats at a 45 angle with a corse file then finish up with a finer file. Ive thought about doing that but so far I dont have the guts to do that to a fine barrel.
54Ball,
I believe the transparent purplish blue you call charcoal bluing is generally called “temper blue” or simply “heat blue” and it is very different from the much thicker scale blue generated by charcoal bluing. Temper blue is created at about 600 degrees F. and is the same color found on clock springs, sword blades, etc. where a higher heat would have ruined the temper. On the other hand, charcoal blue results from packing the barrel in charcoal (to form a lower oxygen atmosphere, and heating it to about 900-1000 degrees for a period of time sufficient to build up a tough gray-blue scale on the surface.
Temper blue wears away from unprotected areas and either one will eventually revert to the more stable brown oxide, rust, over time. As a good friend of mine, with a lot of experience in metal conservation, says, “All iron, and steel, is turning back into iron ore. How long it will takes for this to happen simply depends on the conditions.”
I have worked a lot of wrought iron in both barrels & locks and there is very little difference in the surface color, or appearance, of good quality wrought iron and modern mild steel. Look at some of the brightly polished locks on some European guns.
The lower grades of wrought iron do show a “grain” because of the silicon inclusions but that cheaper iron was more often used on wagon tires and ship’s anchors. When you see grain, especially spiral grain, in a gun barrel it is usually intentional and decorative. I don’t recall ever seeing a longrifle with a twist welded barrel unless the barrel was of a European gun.
When people talk about wrought iron being more rust resistant than modern steel they are usually referring to specifications related to structural use like bridges and steam boilers. The property they are often misunderstanding, in thinking this would apply to a gun barrel, is that wrought iron rusts about as quickly as mild steel but because of the silicate inclusions the rust doesn’t scale away as fast. Therefore the wrought iron forms a layer of rust that helps protect the underlying iron from further rusting. Years ago this property was duplicated in modern steel by adding some copper alloy and it was used for some buildings with external iron framing.
Gary