Hamon: Thing of Beauty of flaw in final finish?

Magnaminous_G said:
The real reason why you don't see many knives with differential heat treating is because it's practically useless on a blade as small as a knife. They differentially heat treated swords back in the day because of an age-old problem: make it hard, and the edge will be sharp and strong but the sword will break if it impacts too much armor. Make it soft, and the edge will not last but the sword will be tough enough not to break. Differential heat treating solved that problem by making the edge hard and the spine tough enough to absorb blows.
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Actually you see it on lots of smaller Japanese knives and tools as well, but I think it's done cosmetically in many of those cases. However, a blow doesn't need to be involved for differential heat treatment to be useful--it helps a bit with lateral strain as well. But I agree that it has more profound effect on larger blades where the forces are more significant.

Honestly I think that with modern metallurgy and heat treatment it's not normally necessary to go differential even with large blades. Hard edges can still chip half-moons when impacted, and if one goes up through the hamon the blade is usually dead because the spine isn't hard enough to carry an edge. Either way it makes for a lot of work to fix and significant blade loss.
 
Differentially heat treated blades will bend before a fully hardened blade, and a fully hardened blade may not bend noticeably at all before it breaks. It all depends on what one wants in a knife. Differentially hardened blades are not stronger, they just bend before they break.
 
I dont like hamon on my yanagi, but maybe because I like the pure mirror finish.

higher grade yanagi dont have hamon due to not having clad shell.
 
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