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In swordsmithing, (from
Japanese Japanese may refer to: * Something from or related to Japan, an island country in East Asia * Japanese language, spoken mainly in Japan * Japanese people, the ethnic group that identifies with Japan through ancestry or culture ** Japanese diaspor ...
, literally "edge pattern") is a visible effect created on the blade by the hardening process. The hamon is the outline of the hardened zone () which contains the cutting edge (). Blades made in this manner are known as differentially hardened, with a harder cutting edge than spine () (for example: spine 40 HRC vs edge 58 HRC). This difference in hardness results from clay being applied on the blade () prior to the cooling process (
quenching In materials science, quenching is the rapid cooling of a workpiece in water, gas, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, suc ...
). Less or no clay allows the edge to cool faster, making it harder but more brittle, while more clay allows the center () and spine to cool slower, thus retaining its resilience.Smith, Cyril Stanley (1968). ''A History of Metallography''. MIT Press. pp. 40–57. ''Hamon'' does not refer to the white area on the side of the blade. The white part is the part that is whitened by a polishing process called ''hadori'' to make it easier to see the ''hamon'', and the actual ''hamon'' is a fuzzy line within the white part. The actual line of the ''hamon'' can be seen by holding the sword in your hand and looking at it while changing the angle of the light shining on the blade. Hamons were developed by and traditionally found in
Japanese swordsmithing Japanese swordsmithing is the labour-intensive bladesmithing process developed in Japan beginning in the sixth century for forging traditionally made bladed weapons ( ''nihonto'') including ''katana'', ''wakizashi'', '' tantō'', ''yari'', '' na ...
. Similar features are often found in knives and swords from the West and are sometimes called temper lines, although these are not often produced with clay but by other means such as partial quenching, flame hardening, or differential tempering, which produces many differences from a traditional hamon. A true hamon, and many of its key features such as a , have no direct translation into English, thus the Japanese terms are usually used when referring to clay-quenched blades.


Introduction

The hamon of a blade is created during the
quenching In materials science, quenching is the rapid cooling of a workpiece in water, gas, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, suc ...
process (). During the differential heat treatment, the clay coating on the back of the sword reduces the cooling speed of the red-hot metal when it is plunged into the water and allows the steel to turn into pearlite, a soft structure consisting of
cementite Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, b ...
and
ferrite (iron) At atmospheric pressure, three allotropic forms of iron exist, depending on temperature: alpha iron (α-Fe, ferrite), gamma iron (γ-Fe, austenite), and delta iron (δ-Fe, similar to alpha iron). At very high pressure, a fourth form exists, ...
laminations. On the other hand, the exposed edge cools very rapidly, changing into a phase called martensite, which is nearly as hard and brittle as glass. The hamon outlines the transition between the region of harder
martensitic Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation. Properties Mart ...
steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
at the
blade A blade is the Sharpness (cutting), sharp, cutting portion of a tool, weapon, or machine, specifically designed to puncture, chop, slice, or scrape surfaces or materials. Blades are typically made from materials that are harder than those they a ...
's edge and the softer pearlitic steel at the center and back of the sword. This difference in hardness is the objective of the process; the appearance is purely a side effect. However, the aesthetic qualities of the hamon are quite valuable—not only as proof of the differential-hardening treatment but also in its artistic value—and the patterns can be quite complex. In English, the terms "hamon" and "temper line" are sometimes used interchangeably, although subtle differences do exist, but both tend to refer to the entire line. In Japanese, however, "hamon" refers strictly to the pattern along the length of the blade, whereas the hamon at the tip () is called the .


Types

The shape of the hamon is affected by many factors, but is primarily controlled by the shape of the clay coating at the time of quenching. Although each school had its own methods of application, and kept secret the process, the exact mixture of the clay, the thickness of the coat, and even the temperature of the water, the clay was usually applied by painting it on in very thin layers, to help prevent shrinking, peeling, and cracking as it dried. Often, the clay is applied to the entire blade by piling up the layers very thickly over the entire sword, and then the clay was carefully cut away from the edge. However, in ancient times tempering was rarely used in Asia, and a fully exposed edge would cool too fast and become far too brittle, thus a thinner layer of clay was usually applied to the edge so as to achieve the correct hardness upon quenching without the need for tempering afterwards. The smith shapes the hamon at the time of coating the blade. There are two basic styles, which are "straight edge" () and "irregular pattern" ( or ). Straight-edge hamons simply follow the edge of the sword with little deviation, except at the tip. This was by far the most popular style in every era and in every province, whereas the more complex patterns that were in themselves works of art tended to be reserved for the wealthy and elite. Straight patterns are usually classified by the width of the hardened zone (), and divided into "wide" (), "medium" (), "narrow" (), and extremely narrow or "string" () hamons. Conversely, irregular hamons do not simply follow the edge, but deviate from it considerably in various ways. The two main groups are "undulating" or "wavy" () and tooth-like or "zig-zag" (), and these are often classified by the
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
or breadth of the irregularities. Sometimes hamons can consist of one style, a mixture of two, or all three (e.g. , , , etc.), with many other differences sometimes added in for effect. resembled saw teeth, whereas resembled horse teeth. consists of multiple sizes and shapes of teeth mixed with areas of regularly sized and shaped teeth. appears as a combination of tooth and wave, resembling rows of plunging
breaking wave In fluid dynamics and nautical terminology, a breaking wave or breaker is a wave with enough energy to "break" at its peak, reaching a critical level at which linear energy transforms into wave turbulence energy with a distinct forward curve. ...
s. consists of waves with wide valleys and steep crests, and were mainly found on swords of the
Muromachi period The , also known as the , is a division of Japanese history running from approximately 1336 to 1573. The period marks the governance of the Muromachi or Ashikaga shogunate ( or ), which was officially established in 1338 by the first Muromachi ...
. The specific shape and style of the hamons were often unique and served as a sort of signature of the various swordsmithing schools or even for individual smiths that produced them. originated with Osafune Kagemitsu and was carried on by Kunimitsu, whereas (very orderly and pointed peaks) were mainly found on swords of the Sue-Seki school. On the most ancient swords, the hamon typically ended just before the sword guard, but on most later and contemporary swords the hamon extends far past the guard, under the handle, and ends with the tang, which provided added strength to the tang. The shape of the hamon is affected by other factors as well. If a sword is made of a composite steel (as most ancient swords were) consisting of alternating layers of steel with different carbon contents, then the steel with higher hardenability will change into martensite deeper underneath the clay coating than the lower-carbon steel. This leaves a pattern of bright streaks that jut a short distance away from the hamon, called , which give it a wispy, misty, or foggy appearance. Likewise, complex swords that consist of sections of different steels welded together may show evidence of the welds near the hamon.Smith, Cyril Stanley (1960). ''A History of Metallography''. MIT Press. pp. 50–52, 57–61.


Origins

China was the first country to produce iron in Asia, around 1200 BC. The Chinese developed
cast iron Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...
, and from this developed processes of making
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...
,
mild steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
, and
crucible steel Crucible steel is steel made by melting pig iron, cast iron, iron, and sometimes steel, often along with sand, glass, ashes, and other fluxes, in a crucible. Crucible steel was first developed in the middle of the 1st millennium BCE in Sout ...
. For a period of over 1000 years, from the first to the eleventh century, China was the world's largest producer and exporter of steel and iron. Nearly all metals then were imported into Japan from China, through Korea, including swords and weapons. Iron-making technology was typically a closely guarded secret, but was eventually imported into Japan from China around 600 or 700 AD, albeit with only a small amount of information to build on, so the ancient smiths began by trying to
reverse engineer Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompl ...
the Chinese methods, coming up with very different processes in the end.Smith, Cyril Stanley (1960). ''A History of Metallography''. MIT Press. p. 41 The Chinese swords had edges made of crucible steel similar to the metal found in Damascus swords, which were welded to a back of soft iron, to give both a hard and strong cutting edge but keeping the rest of the sword soft to prevent breakage. These produced a very hard and visible patterned-edge with a very visible transition at the weld, due to the different composition of the steels, despite the lack of any form of heat treatment. In tying to imitate the Chinese swords, the Japanese came up with unique processes and their own methods of creating a visible hardened edge, taking the Chinese methods and "refining them beyond recognition". The earliest swords forged in Japan ( and ) reflect the similarities between the Japanese and Chinese swords of the time. According to legend, Amakuni Yasutsuna developed the process of differentially hardening the blades around the 8th century AD, around the time that the (curved sword) became popular. The emperor was returning from battle with his soldiers when Amakuni noticed that half of the swords were broken: Although impossible to ascertain who actually invented the technique, surviving blades by Amakuni from around 749–811 AD suggest that at the very least Amakuni helped establish the tradition of differentially hardening the blades. In the most ancient swords, all hamons were of the straight-edge variety. Irregular patterns started to emerge around the 1300s, with famous smiths such as Kunimitsu, Muramasa, and
Masamune was a medieval Japanese blacksmith widely acclaimed as Japan's greatest swordsmith. He created swords and daggers, known in Japanese as ''tachi'' and ''tantō'', in the Japanese sword#Classification by School, ''Sōshū'' school. However, many ...
, among many others. By the 17th century, hamons with various shapes in them became common, such as trees, flowers, rat's feet, clovers, pillboxes, and many others. Common themes included (multiple, overlapping clovers), (
chrysanthemum Chrysanthemums ( ), sometimes called mums or chrysanths, are flowering plants in the Asteraceae family. They are native to East Asia and northeastern Europe. Most species originate from East Asia, and the center of diversity is in China. Co ...
s floating on a stream), (
cherry blossom The cherry blossom, or sakura, is the flower of trees in ''Prunus'' subgenus '' Cerasus''. ''Sakura'' usually refers to flowers of ornamental cherry trees, such as cultivars of ''Prunus serrulata'', not trees grown for their fruit (although ...
s on the
Yoshino River The Yoshino River (吉野川 ''Yoshino-gawa'') is a river on the island of Shikoku, Japan. It is long and has a watershed of . It is the second longest river in Shikoku (slightly shorter than the Shimanto), and is the only river whose watershe ...
), or ( maple leaves on the Tatsuta River). By the 1800s, with the addition of decorative forging techniques, hamons were being created that depicted entire landscapes. These often depicted specific scenery or
skyline A skyline is the wikt:outline, outline or shape viewed near the horizon. It can be created by a city's overall structure, or by human intervention in a rural area, rural setting, or in nature that is formed where the sky meets buildings or the ...
s familiar in everyday life, such as specific islands or mountains, towns and cities, grassy countrysides, or violent crashing waves in the ocean complete with sandy beaches and spraying surf. A common such design was (Priest Saigyo viewing
Mount Fuji is an active stratovolcano located on the Japanese island of Honshu, with a summit elevation of . It is the highest mountain in Japan, the second-highest volcano on any Asian island (after Mount Kerinci on the Indonesian island of Sumatra), a ...
). Sometimes low spots were cut into the clay to produce disconnected from the hamon in the center of the blade, creating the appearance of stars, clouds, wind-blown snowy peaks, or even birds in the sky.


Modern reproductions

Many modern reproductions do not have natural hamon because they are thoroughly hardened monosteel; the appearance of a hamon is reproduced via various processes such as acid
etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other type ...
, sandblasting, or more crude ones such as
wire brush A wire brush is a tool consisting of a brush whose bristles are made of wire, most often steel wire. The steel used is generally a medium- to high-carbon variety and very hard and springy. Other wire brushes feature bristles made from bras ...
ing. Some modern reproductions with natural hamons are also subjected to acid etching to enhance their hamons' prominence. A true hamon can be easily discerned by the presence of a , which is a bright speckled line a few millimeters wide, following the length of the hamon. The is one of many features of Japanese swords that are sensitive to the viewing angle, seeming to appear and disappear when moved with respect to the light. Between the hardened edge and the hamon, the creates the actual boundary between the martensite and the pearlite, but is indistinguishable from the martensite in direct light. It is typically best viewed at long or grazing angles where it appears brighter than the hardened edge. The cannot be faked with etching or other methods. When viewed through a magnifying lens, the appears as a sparkly line, being made up of many bright martensite grains which are surrounded by darker, softer pearlite. Many modern blades, especially those produced in Europe and the Americas, have hardened edges that are made using very different methods than insulating the blade with clay. The most common of these was independently discovered after the invention of the oxy-gas torch. Flame hardening is a method of rapidly heating only the edge with a torch and then quenching before the heat can thermally conduct to the rest of the blade. This creates a very hard edge without affecting the hardness of the rest of the blade, and upon polishing will leave a very visible transition between the harder and softer metals (usually martensite and tempered martensite rather than pearlite). This transition resembles a hamon and may sometimes be referred to as such, but is more commonly called the "temper line" (although it is actually produced upon quenching rather than tempering). A flame-hardened temper line is easily discernible from a true hamon, which produces a nioi that provides a very tough boundary between the martensite and the pearlite. Flame hardening lacks a nioi and instead produces a very brittle zone between the harder and softer metals, called the
heat affected zone In fusion welding, the heat-affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which is not melted but has had its microstructure and properties altered by welding or heat intensive cutting operations. The heat ...
(HAZ), caused by internal stresses and extremely rapid cooling between the hot and cold areas. Therefore, while flame hardening and temper lines are common in hand-made knives, they are rarely found in swords or weapons where a lot of shear and impact forces may be encountered.''Steel Metallurgy for the Non-Metallurgist'' By John D. Verhoeven – ASM International 2007 p. 51


See also

*
Glossary of Japanese swords This is the glossary of Japanese swords, including major terms the casual reader might find useful in understanding articles on Japanese swords. Within definitions, words set in boldface are defined elsewhere in the glossary. A * – thin line ...
*
Pattern welding Pattern welding is a practice in sword and knife making by forming a blade of several metal pieces of differing composition that are forge-welded together and twisted and manipulated to form a pattern. Often called Damascus steel, blades forged ...


References

{{Reflist


External links


Cheness Inc page about Hamons and how to differentiate fakes


Japanese swords