For Ages, The Hamon Has Fascinated Makers And Knife Users Alike. Finicky, Beautiful, And Historic, The Hamon Continues To Wow.

It stretches much if not most of the blade’s length, and when it appears it’s accompanied by an air of mystery, of the exotic. Its contours are created by the knifemaker, and it has always served as a focal point for function and aesthetics. But exactly what is it?

For ages, the hamon has fascinated craftsmen and cutlery users alike.

“Technically, the hamon is the differentiation line between the hardened martensitic edge and the ‘not hardened’ body of the blade,” explained ABS master smith Brion Tomberlin. “The term temper line has been around for years, and, in my opinion, is not correct. Temper refers to drawing back the hardness of the hard martensite after quenching to reduce brittleness and impart toughness. So, a hamon is not a line where temper starts and stops.”

Elaborated knifemaker Joel Mercier, “Tempering refers to the action of heating a quenched steel to a given temperature to remove the brittleness induced by the newly formed martensite, the hard steel molecules created when a steel is quenched. Untempered martensite is very hard but also brittle as glass. It is possible to temper various zones of a blade at different temperatures.”

The hamon is an indicator of the hardening difference between the edge and the softer areas of a blade. These areas are not developed during the making of the steel itself, and a hamon may be formed with stock removal or forged steel.

The hamon comes to life in the quenching process. By achieving different cooling rates, makers form various quantities of martensite, hence a varied hardening of the steel. The faster the steel cools, the higher the percentage of martensite.

The appearance of the hamon denotes a harder edge and a tougher spine in the blade, allowing for flexibility while preserving sharpness and cutting ability. “The hamon,” related knifemaker Johnny Raymer, “is the visual representation of the transition zone between the hardness levels in a differentially heat treated blade. A temper line is often visible within a hamon and is the boundary in which the most drastic change in hardness occurs.”

Along with the functional aspect of the hamon, there is an artful attractiveness. Raymer explains that the hamon extends beyond the temper line itself to the further reaches of the blade during the blending of hardness levels. Most often this is seen toward the edge, yielding a smoky appearance and becoming the hamon’s most artistic component.

How Do You Make A Hamon

Developing a hamon depends on controlling the cooling of the steel as necessary. The rate of cooling is typically determined with the use of clay or another suitable material.

“First, you need to consider your steel selection,” Tomberlin advised. “You need a steel that is low alloy and has a low manganese content. Manganese promotes deep hardening, and the more manganese you have in the steel, the less hamon formation will occur. The most common modern steels that fill the bill are 1095, W1, W2, and 1075, and before the steel is quenched a coating of clay of some sort is applied to the surface that you intend to be less hard. The clay slows down the cooling process in that area.”

Once a blade has been forged or stock removed, Tomberlin takes it to a 120-grit finish that will allow the clay to stick. He thoroughly cleans the blade to remove any oils and then applies the clay. He prefers satanite refractory mortar and learned to use it from now-retired ABS master smith Don Fogg years ago. However, fireplace mortar or certain types of cement, Rutland for example, will also work.

When a light coating of clay is applied, the maker can manipulate the pattern of the hamon. For quenching, Tomberlin uses Park’s 50 oil. Water is an alternative but it takes practice and may produce cracks. “It isn’t for the faint of heart,” he commented.

After quenching, a quick grind at 120 grit will reveal the hamon. Telltale signs that the process has gone awry include the absence of activity—a consequence of the blade being too hot at the moment of quenching. If the hamon runs off the edge of the blade or falls below the pattern of the clay, it indicates that the clay coating was too thick or the blade was not hot enough to perfect the process.

A fine example of a Tomberlin hamon is seen in his chef’s knife with a seven-inch W-2 blade, exhibition thuya wood burl handle, G-10 spacers, and silicon bronze accent. The hamon is subtle yet striking and reaches toward the blade edge in a stunning display.

Raymer adds that the temper line is the boundary of differential hardening, but also notes that it may be more visible in some cases than others. 

“It is almost always unbroken, but as far as being clear and well defined, that is not always the case,” he observed. “Depending on the etching or polishing process you can get multiple results for the visual aspect of the hamon, as well as multiple temper lines depending on the hardened areas.

“Etching for a stark contrast with dark smoked or bled-out areas in the ashi* region of the hamon is very popular. But the hamon can also be given a frosted appearance with etching or simply polishing to give it a subtle ebb and flow that is only seen as the hamon catches light.

“As far as a well-shaped pattern, the hamon is very controllable by the artist crafting the blade,” Johnny maintained. “It could be as systematic or symmetrical or as organic and free as the craftsman desires. The most important objective, as with many aspects of knifemaking, is symmetry from one side of the blade to the next.”

Raymer reveals his skills with the creative hamon achieved on a 5.25-inch blade fashioned from 1095 steel accompanied by a magnificent 11-layer handle consisting of brass, G-10 spacers, Tasmanian blackwood and black ash burl. The overall length is 10 inches, and the knife is accompanied by a sheath in seven or eight-ounce leather with a multi-directional belt attachment.

Those who work in stock removal and wishing to try the hamon technique can take heart. “Forged blades and stock removal knives have the same potential for hamon activity in my opinion,” Johnny stated. “All knives become stock removal at some point. The heat treatment is the same for me in a stock removal knife as well as a forged knife.”

Mercier calls the maker’s manipulation of the hamon the most interesting part of the process. “I have yet to ‘crack the hamon code,’” he advised. “There are many variables at play here, all of which will dictate where and how the hamon will show. The geometry of the blade, the steel used, the type and thickness of the clay, the temperature of the steel, the type and temperature of the quenchant, a vertical or horizontal quench, and more.

“I don’t believe there are better shapes for a hamon. As for the location, I would say it depends on the type of blade and how crucial the hamon is. For example, a hamon is more of a question of aesthetics on a kitchen knife than it is on a weapon. A hamon done properly will show three zones very clearly—high, medium and low martensite areas—and it won’t get too close to the edge of the blade.”

Mercier showcases his hamon technique with a fighter sporting a W2 steel blade, wrought iron guard and buttcap, copper fittings, and curly maple handle. The hamon is well defined and distinctive, clearly marking the effects of the differential quenching process.

“A hamon has nothing to do with forging steel,” Joel agreed. “It all happens during quenching, no matter whether the blade is forged or done by stock removal. If the wavy line of the hamon drops down below or into the blade edge, it means that area will be softer and will compromise the edge performance. Many things can be responsible for this, such as a quenching temperature that is too low, clay that is too thick or too low on the blade, or a quenchant that is too slow. I believe the most common mistake new makers do is using too much clay.”

 The Visual Beauty Of The Hamon

In the end, the development of the hamon primarily adds another dimension to the visual presentation of the knife. It certainly denotes a maker’s skill and attention to the need for a tough spine and an edge that maintains its sharpness without being too brittle.

“Hamons themselves are just an aspect of art,” Raymer reasoned. “The process of differential hardening is beneficial in creating a blade that can take more impact like those seen in fighting knives or choppers, but still performs cutting tasks proficiently. This hardening method allows the knife to spring and/or bend without shattering and without reducing edge performance.”

The hamon, therefore, is representative of the highest performance in blade steel, a visual cue to the user to have confidence in the knife’s ability to undertake the task at hand.

*Ashi refers to the area of a hamon’s lines or shapes that descend toward the edge, and are created by thin strips of clay applied during the coating process.

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