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Comment by Ron Cooper on February 19, 2014 at 15:41

Thanks for your response, Seth! And thanks also for that video (My daughter's name is Monica). 

I had heard the term "differentially hardened" before, but I had no idea how that feat was accomplished. Now, thanks to your explanation and the video, I know that the blade is coated with satanite (clay) in order to control how fast or slow it is cooled during the quenching process.

No clay = faster cooling = higher HRC & more brittle ~ versus ~ Add clay = slower cooling = less HRC & more resilience. 

And, I also learned that the artistry of the hamon line is determined by where, and how much, clay is applied. Very cool!

Thanks, Seth! Your explanation has really given me an excellent window in which to view your art. Also, a much greater appreciation for what folks like you and Randy are doing to raise the bar in the ancient art of knifemaking. Amazing stuff you guys are doing!

Cheers, my friend!

KnifeMaker Comment by Seth Ellis on February 19, 2014 at 9:41

Great question Ron! You are correct in the fact that a hamon is created during the heat treat process. A hamon is an aesthetic byproduct created while deferentially heat treating a knife. The reason for a differential heat treat is that it creates a hard edge a springy center and a soft back imparting more strength to the blade than a full quench. A blade that is full quenched would have the same rockwell hardness from edge to spine and would therefore be brittle and prone to snapping if used to pry.You know the old saying ( A knife is the least useful and most expensive pry bar you will ever break.)  In order to create a hamon before, I quench the blade in oil, I coat it with a special clay known in the industry as satanite. This protects parts of the blade from hardening when it's quenched. depending on where and how heavy the clay is coated.

Here's a link to a video I created for a customer of mine that shows the process in action.

http://www.youtube.com/watch?v=zlooa8EAeX8

 

Comment by Ron Cooper on February 19, 2014 at 3:43

Seth, not being a knifemaker, myself, I am curious about how the hamon is actually created. Is it during the heat treatment that cutting edge is given the extra hardness? It's certainly a beautiful knife! You could probably get two fingers into that choil for some real close-up work. Sweet!