I wonder even more about at what time the twist-core pattern-welding first appeared in this area. In the example I presented in
this thread, when I removed the broken shaft elements, the tarry mastic was still in place and there was old brown rust on the tang - and no evidence of recent corrosion products or of debris to suggest that this was also its state when it was mounted - likely a century ago. The nature of the oxide layer on the tang resembled the same patina often seen on a Japanese swords that are several centuries old.