I thought this was well known already?
Williams began to test the Ulfberht blades when a private collector brought one into the Wallace, and found they varied wildly. The tests at the NPL have proved that the inferior swords were forged in northern Europe from locally worked iron. But the genuine ones were made from ingots of crucible steel, which the Vikings brought back from furnaces thousands of miles away in modern Afghanistan and Iran. The tests at Teddington proved the genuine Ulfberht swords had a phenomenally high carbon content, three times that of the fakes, and half again that of modern carbon steel.
The crucible steel against locally worked iron, perhaps not, but the high carbon content I thought was well known. That\’s what made Damascus steel so desirable for example, that it had a very high carbon content (manufactured, I think, by continual reforging, wasn\’t it?).