Mokume-gane

Mokume-gane (木目金) is a Japanese metalworking procedure which produces a mixed-metal laminate with distinctive layered patterns; the term is also used to refer to the resulting laminate itself. The term mokume-gane translates closely to 'wood grain metal' or 'wood eye metal' and describes the way metal takes on the appearance of natural wood grain. Mokume-gane fuses several layers of differently coloured precious metals together to form a sandwich of alloys called a "billet." The billet is then manipulated in such a way that a pattern resembling wood grain emerges over its surface. Numerous ways of working mokume-gane create diverse patterns. Once the metal has been rolled into a sheet or bar, several techniques are used to produce a range of effects.

Mokume-gane has been used to create many artistic objects. Though the technique was first developed for production of decorative sword fittings, the craft is today mostly used in the production of jewelry and hollowware.

History

The name characterizes the typical appearance of the forged pieces. Mokume (木目, literally "wooden eyes") means "wood grain," and Kane (金) means "metal." Parallel styles also emerged: Itame-Gane (板目金, eye-shaped pattern) and Masame-Gane (正目金, parallel pattern). The additional designation, Mokume-Gane Damascus, comes from the European-influenced visible cross pattern, although this is a European neologism.

The starting material for these techniques, also known as a layered block, is made from thin metal plates that are welded together by forging, as in the production of Damascus steel. In Mokume-Gane, metals and metal alloys are preferably combined to produce a pattern with the highest possible contrast. It is important that the metals used have similar physical properties such as hardness and melting temperature, as the welding of the metal plates takes place just below the melting temperature. Typical alloys in Japanese blacksmithing include shakudō, shibuichi and kuromidō. Gold and silver were rarely used at first, as these alloys were preferred. A modern material of European origin is Corinthium aes. Once the layered block is produced, it receives its individual pattern through diverse further processing using a variety of forging, etching and engraving techniques. 

Due to the highly developed forging technology and the readily available colored metal alloys, the Mokume-Gane technique became widespread in Japan. Today, this very complex and expensive forging technique is used only by a few gold and silversmiths to create individual pieces of jewelry.

Origins

First developed in 17th-century Japan, mokume-gane was originally used for swords. As the customary Japanese sword stopped serving as a weapon and became largely a status symbol, a demand arose for elaborate decorative handles and sheaths.

In the Edo period, when the world was at peace, the Japanese sword as a weapon began to be decorated as a symbol of the samurai. In the early Edo period, sword fitting craftsmen began to decorate the tsuba (guard) and kozuka (guribori). "Guribori" is a technique in which layers of different colored metal are forged together and then engraved into the metal layers to reveal the underlying colored metal. This imitates " Guribori", a carved lacquerware technique, which creates a embossed pattern by carving into layers of lacquer of different colors. 

Mokume gane is made by hammering the grooved relief of the guri carving into a flat surface, making the carved areas stand out in comparison. This craft developed during the Edo period, but when the sword ban was imposed in the Meiji period, sword fitting crafts fell into disuse. At the same time, the Mokume Gane technique became known outside of Japan along with the export of Japanese swords overseas. 

To meet this demand, Denbei Shoami (1651–1728), a master metalworker from Akita prefecture, invented the mokume-gane process. He initially called his product guri bori, as the technique in its simplest form resembled guri, a type of carved lacquerwork with alternating layers of red and black. Other historical names for it were kasumi-uchi (cloud metal), itame-gane (wood-grain metal), and yosefuki.

The early components of mokume-gane were relatively soft metals and alloys (gold, copper, silver, shakudō, shibuichi, and kuromido) which would form liquid phase diffusion bonds with one another without completely melting. This was useful in the traditional techniques of fusing and soldering the layers together.

Over time, the practice of mokume-gane faded. The katana industry dried up in the late 19th century, with the Meiji Restoration returning ruling power to the emperor, following the dissolution of the shogunate government and the end of the samurai class. The public display of swords as a sign of samurai status was outlawed. After this, the few metalsmiths who practiced mokume-gane along with most other sword related artisans largely transferred their skills to create other objects.

Adoption of mokume-gane in the West

Tiffany & Co's silver division under the direction of Edward C. Moore began to experiment with mokume-gane techniques around 1877, and at the Paris exposition of 1878, Tiffany's grand prize-winning display of Moore's "Japanesque" silver wares included a magnificent "Conglomerate Vase" with asymmetrical panels of mokume-gane. Moore and Tiffany's silver smiths continued to develop its popular mokume-gane techniques in preparation for the Paris exposition of 1889, where it displayed a vast array of Japanesque silver, using ever more complex alloys of shakudō, sedo and shibuichi, along with gold and silver, to make laminates of up to twenty-four layers. Tiffany's display again won the grand prize for silver wares, and the company continued to produce its Japanesque silver with mokume-gane techniques up into the 20th century.

20th-21st century development

By the mid 20th century, mokume-gane had fallen into heavy obscurity. Japan's movement away from traditional craftwork, paired with the great difficulty of mastering mokume-gane, had brought mokume-gane artisans to the brink of extinction. It reached a point where only scholars and collectors of metalwork were aware of the technique. It was not until the 1970s, when Hiroko Sato Pijanowski – who learned the craft from Norio Tamagawa – that the craft was reignited in the public eye, as Hiroko and her husband Eugene Pijanowski brought the craft of mokume-gane back to the United States and began teaching it to their students.

Hiroko Sato and Gene Pijanowski had been working with layered metals in the USA since 1960, using sheet metal soldered together in layers. Whether intentionally or by chance, both learned about Mokume-Gane, a process traditionally used in Japan, and acquired the necessary basic technical knowledge, which they subsequently developed further and expanded the field of application of Mokume-Gane to include tools and jewelry. Around 1970, the American George Sayer developed bars made of soldered metal layers, a development that was further advanced by Steven D. Kretchmer, who also came from the USA and had learned about Hiroko Sato and Gene Pijanowski's process there in 1980, with the development of stampable, easy-to-work gold Mokume-Gane alloys without solder. Among the first European Mokume-Gane smiths, the specialist literature includes Alistar McCullum, England, who began working with Mokume-Gane in 1978, as well as the Dutchwoman Birgit Laken, who learned the technique from Alistar McCullum and then pursued her own further developments, especially from an artistic point of view.

The integration of Asian elements is also being implemented by many gold and silversmiths, partly to open up new market segments, and partly through a return from mass-produced goods to high-quality individual pieces, partly out of a passion for craftsmanship, partly for profit optimization. Due to the growing demand for prefabricated material, as of 2008, most precious metal semi-finished products companies offer sheets, strips, tubes, wires, rods, and cast materials in the Mokume-Gane segment.

The Mokume Gane trend among numerous blacksmiths in Germany was largely triggered since 2004 by the company Schichtwerk  and promoted by C. Hafner and their presentation of the Schichtwerk modules at the Inhorgenta 2005, which can be clearly seen in the number of German Mokume Gane Damascus blacksmiths and the first associations that were forming. 

Since 2003, foreign goldsmiths such as Chaix and Pijanowski have been offering various silver blocks for the low-price segment, which some German suppliers took up at a time of rising precious metal prices. An independent German approach was implemented in 2007 with the new development of the Saarland master goldsmith Markus Eckardt Mujodogane. This new development still aimed at significantly reducing costs in the area of layered blocks, although his main focus was also on variable color contrast and ensuring good craftsmanship through the additions. Silver-silver alloys, and especially Mujodogane, allow the considerably more expensive white jewelry metals such as white gold, palladium, and platinum to be completely replaced visually, without compromising on the craftsmanship. Mokume blocks made of silver represent something new only in the Mokume-Gane field, as the smiths initially followed the original Japanese tradition of the non-ferrous metal block. However, rising raw material prices in the precious metals sector inevitably made a non-ferrous metal substitute necessary for the low-price segment. Snow gold,  a white/grey gold alloy, may contain silver, but belong to the medium to high-price segment.

By using hydraulic presses and the diffusion welding process, German Mokume Gane artists began experimenting with the non-traditional metals iron and titanium for Mokume Gane in 2006. This development originated in the USA with the Mokume Gane artists Binnion & Chaix, 2002. One argument in favor of titanium is that in many non-ferrous metals, an iridescent effect can be created through the formation of a translucent oxide layer in conjunction with hot corrosion, and thus different color lusters arise through the refraction of light in these layers, such as a violet luster in copper. However, the resulting colors are not as differentiated as is the case with anodizing titanium.

In 2015, the first scientific study of the Chair of Materials Science (WKK) at the Technical University of Kaiserslautern was published, in which the effectiveness of the manufacturing methods of fire and diffusion welding and their effects on the metal structure of Mokume Gane were investigated.

Present day

Today, jewelry, flatware, hollowware, spinning tops and other artistic objects are made using mokume-gane.

Modern processes are highly controlled and include a compressive force on the billet. This has allowed the technique to include many nontraditional components such as titanium, platinum, iron, bronze, brass, nickel silver, and various colors of karat gold including yellow, white, sage, and rose hues as well as sterling silver. At the Santa Fe Symposium, a major annual gathering of jewelers from around the world, there have been several papers presented on new, more predictable, and more economic, methods of producing mokume-gane materials, along with new possibilities for laminating metals such as the use of friction-stir welding.

Techniques

Processing procedure

A block made of layers of copper, silver, red copper, nickel silver, and brass forged together.

1. Different colored metals are layered and forge welded (heated and pressed) to create a laminated block.

This step is the most important and requires the highest level of forge welding skill. In recent years, instead of forge welding, other procedures such as soldering the layers together or pressure welding (heating and applying pressure in a furnace) have been used. 

2. The engraving process, in which a chisel is used to carve the piece and expose the underlying colored gold (this is called "guribori").

3. The engraved metal is hammered flat to make the lower and uppermost layers of Irogane flush with each other.

Repeating steps 2 and 3, the piece is finished into a complex pattern. In addition to carving, the piece may also be twisted or bent, then flattened.

4. The difference in color of the finished Mokume Gane can be seen even in its raw form, but the Niiro finish creates contrast by oxidizing the surface and bringing out the color. In the case of Mokume Gane with different gold shades (gold, red gold, white gold, etc.), the Niiro finish is not used.

Liquid phase fusion (historic)

In liquid phase fusion, metal sheets were stacked and carefully heated; the solid billet of simple stripes could be forged and carved to increase the pattern's complexity. Successful lamination using this process requires a highly skilled smith with a great deal of experience. Bonding in the traditional process is achieved when some or all of the alloys in the stack are heated to the point of becoming partially molten (above solidus) this liquid alloy is what fuses the layers together. Careful heat control and skillful forging are required for this process.

Soldering (brazing)

In attempting to recreate the appearance of traditional mokume-gane, some artisans tried brazing layers together. The sheets were soldered using silver solder or some other brazing alloy. This technique joined the metals, but is difficult to perfect, particularly on larger sheets, because flux inclusions can get trapped or bubbles could form. Commonly, these imperfections need to be cut out, and the metal re-soldered. In addition, brazed sheets also do not display the same levels of ductility and work-ability of diffusion-bonded material.

Solid-state bonding (contemporary)

The modernized process of solid-state bonding typically uses a controlled atmosphere in a temperature-controlled furnace. Mechanical aids such as a hydraulic press or torque plates (bolted clamps) are also typically used to apply compressive force on the billet during lamination. These provide for the implementation of lower temperature solid-state diffusion between the interleaved layers, thus allowing the inclusion of non-traditional materials.

Development of the mokume-gane pattern

After the layer fusion, the surface of the billet is cut with chisel to expose lower layers, then flattened. This cutting and flattening process will be repeated over and over again to develop intricate patterns.

Coloring

To increase the contrast between the laminate layers, many mokume-gane items are colored by the application of a patina (a controlled corrosion layer) to accentuate or even totally change the colors of the metal's surface.

Niiro patination and rokushō

One example of a traditional Japanese patination for mokume-gane is the use of the niiro process, usually involving rokushō, a complex copper verdigris compound produced specifically for use as a patina. The piece to be patinated is prepared, then immersed in a boiling solution until it reaches the desired color, and each element of a compound piece may be transformed to a different color. Historically, a paste of ground daikon radish was also used to prepare the work for the patina. The paste was applied immediately before the piece is boiled in the rokushō to protect the surface against tarnish and uneven coloring.

Similar laminates

Traditional mokume gane is made by joining metal sheets in layers, but other techniques include bundling metal prisms together and heating and pressing them together, as in marquetry, or twisting red-hot rods of different metals together and forging them together. In an accidental but parallel development, Sheffield plate was developed in England. It follows a similar principal of bonded layers, without use of solder, but typically had 2–3 layers, whereas mokume-gane could have many more.

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