The pattern only comes out when the steel is blued or browned. It is only slightly apparent in the steel when
polished, but when chemically "rusted,"the true beauty of the differing qualities of the carbon contents of the
various steels becomes apparent.
The Damascus shotgun barrels where made by hammer welding the pre-damascened metal billet around a
steel mandrel. This particularly fine specimen shows the spiraling nature of the Damascene metal as it was
wound the mandrel from muzzle to breech.
The "lost technique of making Damascus Steel" is a myth. It was never lost, it was merely supplanted by better means of making stronger and better steel for weapons that were safer and longer lasting, if not so beautiful. I tried to find some examples of broken Damascus steel swords, but very few survive as steel was in high demand and value when such weapons were in use, and a broken blade's metal was quickly re-used. However, here are some shotguns that suffer from the problems of Damascus steel aging:
This sample is probably the result of an impurity which caused age
corrosion inside the steel, or too much carbon which impeded hammer welding.
This sample demonstrates clear crystallization between the welds of the Damascened metal,
resulting in complete failure under overpressure from a modern shotgun load.
When I managed a gun shop in my youth, among the horrible examples I kept for hunter and and firearm safety training classes of what NOT to do, I had several Damascus barrel failures to show why you should never attempt to shoot Grampa's old hand-me-down shotgun, no matter how good it looked, especially with modern shotshells. Some of them had mid-barrel blow-outs, ten or more inches beyond the chambers where the metal just failed. Others failed at the breech. One cheap model had literally unwound, failing where the ribbon billet had become corroded between the spirals.
I literally cringed every time I watched the Pawn Stars "experts" claiming that an antique firearm was worth a lot more if they could tell a customer it could still fire, and they'd take it out and fire it, especially an antique shotgun with a Damascus barrel. I never advised shooting fine antiques. There was too much chance of breakage and as long as the mechanism was operational, there was NO additional value in knowing an antique firearm was still fireable. Firing it could crack the metal, the stocks, or irreplaceable springs. In addition, they were literally taking Chum's life in their hands with each trigger pull. If I wanted to shoot antiques, I'd buy a modern reproduction, not shoot the antique.
"Note that while pattern welding did produce stronger barrels in the 1700s and part of the 1800s, the rise of better steel production techniques made this technology somewhat obsolete. Despite popular culture which assumes that pattern welded Japanese samurai swords can cut through anything, the truth is that even a modern spring from a car suspension has better quality steel than an authentic pattern welded Japanese sword from the 1700s/1800s. The same holds true for gun-barrels as well and modern steels far exceed pattern welded steel in hardness, toughness and durability. The extra labor and specialized skills needed to make pattern welded steel barrels also made it less desirable compared to other techniques. Source: Firearms History, Technology & Development
The source for the block quote above has some excellent explanations of how Damascus shotgun barrels are made. Unlike the swordsmiths of Damascus, they use square rods and sheets of iron and steel stacked in patterns which were easier to exclude impurities than round wires which were easier to draw out. The more expensive patterns could also use triangles, rhomboids, hexagonal shapes, etc., anything that could be closely fitted and bundled together before heat and hammer welded, then twisted to produced a unique pattern in the final metal.
Some of the wordsmiths insisted on using charcoal produced only from a specific type of tree for their forges, thinking only that would get what they wanted. in any case, making either swords or Damascus metal of any type was extremely labor and skill intensive and lost out to modern steel formulations and forging. It's now only used for artisan knives and art guns, etc.