Just for everyone's interest, and before everything disappears from PictureTrail
there are rust inclusions
within the barrel wall (not upon the surface
as these appear to be) called "greys"
"Greys" are not rust inclusions. Rust is rust, and "greys" are greys.
"Greys" is a somewhat generic term for various inclusions in both fluid steel and Damascus. Greys may be composed of slag, rolled in scale, or other impurities.
There still seems to be a lot of confusion concerning just what scale is. Mill scale IS NOT burned metal, as was described in the copy-and-paste research. Mill scale is various oxides such as Wustite, hematite, and magnetite, that form on the surface of steel when it is heated above critical temperature, and exposed to atmospheric oxygen. Steel can be heated to very high temperatures without the formation of scale if the heating is done in a controlled atmosphere purged of oxygen. But in the presence of oxygen, scale can and will form at much lower temperatures. Scale is not common red oxide rust (hydrated ferric oxide), and scale can actually prevent rust from forming until the protective layer of scale is broken. Here's a pretty good explanation of what scale actually is composed of:
https://www.ispatguru.com/mill-scale/Slag, scale, and other inclusions end up in steel and iron during the manufacturing process, and various methods are employed to minimize them. Better quality steel will have less inclusions and smaller inclusions. But no steel is ever free of inclusions. Scale forms on the surface, and ends up in steel during the hot rolling or hot forging process. Because of that, most scale within steel will usually be found closer to the surface. Because of the way Damascus is made in layers of welded, folded, and twisted iron and steel, scale may end up anywhere within. When you see videos of Damascus barrel production, you often see the barrel maker applying a fluxing agent such as borax to minimize scale formation. Every time the billet or barrel is returned to the forge for reheating, more scale begins to form. The pounding by manual or trip hammers breaks a lot scale from the surface during the hammer welding, but inevitably, some will end up hammered into the surfaces, and trapped within the welds. Naturally, lesser quality Damascus made by makers with less skill and less effective fluxing will have more scale inclusions.
I don't think we can say that the shiny spots on the barrels in this Thread is solder, silver alloy or otherwise. Unfortunately, the original poster has not returned to provide the information we need to make an accurate determination.
