In sword and knife making, the hamon (刃文, hamon) (from Japanese, literally “blade pattern”) is the visual effect of differential tempering. The hamon is the visual separation between the hardened edge and the softer portions of the blade. In the case of a traditional Japanese clay hardening (Yaki-Tre), the process is be better termed ‘differential hardening’ as it is achieved during the quench / hardening of the blade. A similar effect can also be achieved in the tempering stage by deferentially heating the spine. The term ‘differential temper’ references the result of each method, while the term ‘differential tempering’ refers to the method used. For this discussion, we will focus on clay hardening.
From a functional point of view, differential temper can create a hard edge with a softer shock absorbing spine. The benefit being greater edge retention without having a brittle spine. It is a way of increasing the hardness of the cutting edge while not increasing the tendency of the blade snapping. Like most things in knife and sword making, this comes at a price. A blade that has a soft spine will not spring back when bent. Instead, it will take and hold the bend.
While most commonly associated with Japanese blades, the hamon is becoming more popular among makers of Western style knives. In fact, the functionality of the differential temper has been with Western knife makers via edge quenching for some time. But it is the clay hardening on select steel types which really makes the hamon able to pop with proper finish.
Simple Hamon / Temper Line
Materials and techniques exist to create absolutely eye popping hamons. In Japan, the how of polishing blades and bringing out the hamon were traditions and schools all to their own. The sword maker would bring the hamon out to check his work, but the sword was then handed off to the polisher to finish. I would not call that system mass production, but it does have similarities with modern mass production. By compartmentalizing skill sets, it takes less time to train those who produce the product. Thus, while more staff is required to operate the assembly line, it can be up and running much faster. Additionally, replacing any one individual is easier. This tutorial will focus on the roll of creating the hamon, not polishing it.
Steel Selection – Here is where many knife makers fail before they start. Virtually any medium or high carbon steel can receive a differential hardening or tempering. In fact, while hamons are relatively new to Western style knife making, the practice of edge quenching is not. Remember, the hamon is the visible indication of a differential hardened blade. The steel selection will help determine how visible the hamon can be.
10 Series – The 10 series is very popular among knife makers because it is very forgiving. Because it is forgiving, it is more affordable to work with. Heat treating the 10 series does not require as narrow a range of specific temperatures as do more complex steels. So it is not necessary to purchase a commercial heat treating oven. Hardening may be accomplished with a gas or coal forge. Tempering may be accomplished in a kitchen oven.
W Series – W1 and W2 are also good choices for the creation of hamons. Of the two, W2 seems to produce the most active and vivid effects. The down side to these steels is they are not as forgiving when it comes to forging temperatures. Using a coal forge, it is very easy to overheat these steels. For these and a reason that I will discuss with the quench, 1095 is likely the best choice for your first attempts at hamons.
Wire Wrap (image 1) – Here is a modern trick to help keep tour clay on your blade. Wrapping your blade with thin steel wire will provide an additional foundation for the clay. Depending on how you wrap it, the pattern of the wrapped wire can provide a guide for your clay.
Clay Coating (image 2) – When folk talk about traditional clay hardening, they often think it was done with clay. While clay was often part of the mix, the recipes varied greatly from smith to smith and tradition to tradition. Fortunately for the modern smith, simple refractory cement works fine. It is available at most hardware stores.
Generally, the thickness of the clay should be about 1/8th of an inch. Some smiths choose to water down their clay for a very fine initial coat over the entire blade, let it dry and then apply a thicker coat. This tends to help the clay stick and decrease scaling from the quench.
Quenching – The quench follows regular procedure for simple carbon steels. Heat slightly past non magnetic, soak and plunge. For hamons, I recommended 1095 even though it can be a bit more temperamental than others in the 10 series for a couple of reasons. The first is that like W1 and W2, it can be quenched in water. Due to the speed at which water cools a blade, quenching in water tends to bring out the crispest and most active hamons. The trade off to this is that water is such an aggressive quench it often causes blades to crack. The low cost canola and other oils used by many knife makers do not cool rapidly enough to produce as vivid a hamon if at all. I have found two options.
Interrupted Quench – First into water for a 3 second count. Then into oil to fully cool. Both water and oil should be approximately 130 ° F. If your timing and temperatures are right, the edge will harden in the water quench and the back will cool slowly in the oil quench. If either timing or temperature is off, your hamon might fail in a few different ways. One of which resulting in shards of metal flying threw the air.
Park’s 50 – .This is the safest and most reliable approach. It is also the most expensive. At the time of writing this, Amazon lists it for over $70.00 / gallon. Like water, Park’s 50 cools the blade rapidly for the first few seconds. It then acts more like traditional quenching oils, cooling slower than water. This decreases cracking tremendously.
Hamon with Etch (image 3) – After the blade is quenched and tempered, I tend to clean and sand to about 220 grit to check for hamon. I then dip it in ferric chloride for about 30 seconds, neutralize with baking soda an water, flush with cold water, and verify the hamon developed properly before starting to polish. This can be a huge time saver. Without some form of etch, a hamon does not show itself via sanding and polishing until the much finer grits. If it did not develop in the quench, all that sanding and polishing wont make it show.
Hamon with Light Polish (image 4 & 5) – Photos 4 and 5 show a completed knife with a very mild polish n etch for a couple of reasons. The first being the polishing of a hamon is a subject unto itself. In fact, the art of polishing traditional Japanese blades with hamons is an art of its own. Some claim that the traditional training for polishing a Japanese blade was longer than the training for smithing those blades. The other reason is time consumption and pricing. I priced this knife around $100.00 with leather sheath. Yes, I love making knives. I need to aggressively sell knives to continue to make knives. Price really does matter.
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