So, I recently did a walkthrough for a client and his kids who were curious to see the blade making process and I figured I'd share a bit of it with the OG since I've been asked a number of times. This thread will focus solely on the hamon aspect of the process.
To start off, we have below the blade, guard and handle all finished with pre-heat treat work. At this point, the blade has been forged from a bar of W2 steel and ground to a rough 60 grit belt finish.
Up to this point, we're on the same path we'd take for any given knife. And this is where this particular type of knife diverts from the normal path. From here, I normalize the steel via thermal cycling. Thermal cycling consists of bringing the blade up to a hair below its critical temperature and then allowing it to cool in the air until it can be touched barehanded. This is done three times. The purpose of this process is to ensure that the internal grain structure of the steel is back to its normal state after forging and grinding. This relieves any stresses caused by the forging and grinding processes.
I then move to clay-coating the blade with high-temp refractory clay rated up to 3000deg Farenheit.
Here we have the coated blade. Everything looks a mess, no? That'll change shortly.
The clay is left to start curing overnight. The next day, the blade gets placed with a metal clamp very carefully in the tempering oven at 200deg F for 2 hours to fully harden the clay before heat treatment. The time spent at 200deg F impacts the the normalization process exactly none due to the low temp at which it sits.