Thanks all for such an informative discussion, I am learning quite alot about Japanese swords. I just wanted to add a few cents on fractures and cracks. Of course, cracks follow grain boundaries (back to microstructures again). That said, one of the benefits of crucible steel is the spheroidal cementite. On a microstructual scale a crack would hit the roundish cementite and the stress would dissapate (sorry can't spell, just woke up and still on first cup of coffee), thus stoping the cracking. This all shows how much more work really needs to be done. I too have wondered about the "benefits" of hardness testing to answer archeological/anthropological questions. I think we need some "battles" with high quality authentically replicated swords, but it would be indeed a pity to work such masterpieces until they break!