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Now here is something you don't see every day :)
I was working on a suminagashi blade that hadn't hardened properly along the edge. The reason was I had ground it too thin, and even with the oil tank right next to the forge, I could not get the blade in the tank quickly enough before the air cooled the edge to below critical.
So I thought I would be smart and instead of taking out the blade, I'd take the iron pipe itself out of the fire, and upend it above the quench tank. That way the blade would hit the oil instantly. However, this is the result :)
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I spent yesterday trying to think what had happened, talked it over with a friend of mine who is a master bladesmith, and we came to the following conclusion: The blade fell out of the pipe, immediately hardening the edge. The blade hit the bottom of the tank a split second later, where it made an unholy noise, like water falling into a potato chip fryer. What my friend suggested was that there is likely a thin film of icecold condensation water at the bottom of my quench tank.
When the blade hit the bottom, the side that hit the bottom got a thermal shock that was so bad that it literally tore one side of the razor apart from the other side. The crack goes right through the middle of the core steel because it has less 'give' in it than the mild steel sides. The reason it doesn't fall apart is that thehollow ground part is whole, as well as the tail.
Apart from this minor detail :p the blade came out pretty nicely and I am going to finish it and make scales. Probably use it as a personal blade for a while. Sure it is not perfect but there is no reason to just throw it away either. If anything, it should shave me just fine :)
Anyway, this illustrates perfectly the raw violence of a blade quench. Any force strong enough to rip an entire blade in half, lengthwise has to be respected.