Yes, our hamons are real!
A common question we often get asked is: "are our hamons real?", and the answer is "yes!". We do occasionally do a faux hamon thats etched on the blade, but its always stated that its a faux hamon when we do this, and 99% of the time our hamons are real.
So how is a real hamon line done? Through differentially hardening the blade during heat treatment. Theres a few ways to do differentially hardening but the method we most commonly use is clay coating the blade...just as the Japanese have done for hundreds of years. The clay coat works as an insulating blanket, and when the knives are heated up and quenched in the oil, the clay slows the rate of coolong for the steel under the clay...resulting in softer area under the clay, while having a fully hard edge.
Its a fairly indepth process that you have to get the variables just right to achieve a nice hamon, but thats the gist of it.
I snapped some pics of some of the process in the gallery above. First the blades are rough ground to a bit larger than their final shape, then clay is coated along the spine. The knives are then heated and quenched in oil. After quenching the clay is scraped off, and I grind a bare spot on the blade to see how the hamon looks before tempering. Next are the tempering cycles. Aftet that we start on grinding to the final shape of the blade. After grinding we go to the tedious process of hand sanding the blades to remove any machining marks. Next is the acid etching. We clean the knife well, and dip it in acid for about a minute, then we pull the blade out, neutralize the acid, and polish the blade by rubbing emery powder on it. At this point you can clearly see the hamon. Prior to acid etching you can only see the hamon if you hold it at just the right angle.
Theres various acids that can be used, and various polishing methods. If you use a weaker acid, and short etching times you get a real subtle look...where you have to be looking for the hamon to see it. We use a bit stronger acid, and 3-6 etching/polishing stages to get a nice dark hamon that you can see across the room.
Why does the acid bring out the hamon? Because the steel has different hardnesses and crystal structures after differentially hardening, and the acid affects those areas differently. Resulting in the spine etching deeper, the edge barely being affected and the actual hamon line etching nice and deep.