Mokume-Gane literally translates to mean wood grained metal. The technique of developing a pattern much like wood grain in metal laminae is a result of the principle of diffusion; the bonding of layers of metal, without the use of solder or flux, using at least two different colored metals or alloys compatible in their properties of ductility and malleability. The diffusion occurs by pressure and/or heat, which causes agitation and intermingling of molecules, atoms, ions, etc., at the interfaces of metal and/or alloy sheets. A new molecular crystalline structure is created between each of the laminae or layers, becoming then one homogenous mass. Patterns like wood grain then could be achieved after alternately carving and forging, resulting in topographical patterns. There are no limitations as to size, thickness or pattern. Mokume-Gane can be utilized in metalsmithing, construction, repousse and chasing, or as a material to inlay into or to be inlaid. It can enhance or itself be a piece of jewelry or holloware. In Japan it is primarily used in creating holloware.
Mokume-Gane was innovated by Denbei Shoami (1651-1728), who lived and worked most of his life in Akita Prefecture of Northwest Japan. He was a superb craftsman who was given permission to use the name Shoami from Shoam School, which started in Kyoto in the late 1500's. He was also supported by Satake who was then Kaimyo (feudal lord) in the Akita area. Mokume-Gane was Shoami's invention, but it was only one facet of his work. It should be realized that he was also a historically important craftsman who produced excellent examples in steel, of sword furniture, and sword fittings with carving and inlay. At first, Shoami named his technique Guri Bori because the pattern on his first nonferrous Mokume-Gane tsuba was like Guri, which is one of the Tsuishu techniques in lacquer work (Urshi), originating in ancient China. Tsuishu is one of the techniques where patterns are achieved by carving into thick layers of different colored lacquer; when line patterns are created, it is referred to as Guri. From sword making influences Denbei Shoami found that nonferrous laminates could be joined together to create patterns similar to lacquer work. He later named this pattern Mokume-Gane. His oldest work in Mokume-Gane was used in the Kizuka (sword hilt) using gold, silver, Shakudo, and copper. This technique was also called Itame-Gane or Yosefuki. There is no doubt that Denbei Shoami was influenced by the swordsmith and adapted those principles of forge welding to begin Mokume-Gane.
The reason why this technique developed in Japan was not only because of the highly developed skills in swordmaking, but the understanding of metallurgy and the numerous skills among metalsmiths. The unique existence of colored alloys employed by Japanese craftsmen was a contributing factor as the exchange of information and substantial availability of materials which helped to give birth to Mokume-Gane. There is one example of Mokume-Gane made by Soko Hirata, then a professor in the raising division of the University of Fine Arts in Tokyo in the early 1900's. Sonyusai Yoshida, while a pupil of Professor Hirata, produced a body of work utilizing Mokume-Gane. Yoshida eventually became Professor at the same school. The president of the university, Naohiko Masaki, named the technique Kasumi-Uchi. However, it is generally known as Mokume-Gane today, because the majority of the patterns created emulate wood grain.
There are no known historical examples of this particular method of diffusion of nonferrous materials to produce patterns inherent in the structure, other than in Japan. The closest example would be Sheffield Plate done in the United Kingdom beginning in the 1740's through the 1870's. Sheffield Plate is the cladding of silver over copper or nickel silver (German Silver) and was utilized for an entirely different reason; notably, to reduce the cost of the silver content within a product. Another example of Mokume-Gane would be in the central link of the chain of offices made for the Mayor of Preston, Lancashire, the United Kingdom, by Sir Alfred Gilbert in 1887-88. The process was done by using solder and flux and it is essentially a different approach. In the soldering application of the Mokume-Gane process, problems of air pockets, cracking and peeling occur. Its limitation are basically that it cannot effectively be formed or raised into complex shapes because of the solder itself and the different stresses enjoined in the metal laminae, if not compatible in malleability.
The authors started research into Mokume-Gane in Japan in the early 1970's, after exploring soldered Mokume during the mid to late 1960's. An opportunity to learn and share this technique with Norio Tamagawa, Gyokumei Shindo and Masatoshi Yagihara, has thus propagated the traditional method of Mokume-Gane. A wave of interest has spread among craftsmen of the West because of the similarity in the nature of diffusion, metals and/or alloys that can stick together without solder or flux and will not come apart. Several universities in the United States have researched this method and developed other possibilities in pattern development and utilized new materials, notably the University of Southern Illinois at Carbondale and the University of Michigan. The process involved with creating Mokume-Gane will be introduced in combining the methods innovated in Japan and developed from these traditional methods in the United States.
Copper and Kuromi-do or Shakudo are used as the basic metal and alloys because of cost, malleability and coloring possibilities. However, the combination of materials could be any of the following:
Metal / Color with Rokusho (Japanese Patina) / Melting Point (Centigrade)
Fine Silver / White / 960.5
Sterling Silver / White / 893.
Gold (24k) / Yellow / 1063.
Copper / Orange to Brown / 1084.
Shakudo / Purple Black to Black / 1050.
Good Quality / Gray / 950.
2nd, 3rd Quality / Gray / 900.
Shiro Shibuichi / Light Gray / 850.
Kuro Shibuichi / Dark Gray / 1040.
Kuromi-Do / Dark Brown to Black / 1070.
Composition / 1st Quality / 2nd Quality / 3rd Quality / 4th Quality / 5th Quality SHAKUDO:
Gold (24k) / 4.8% (1st) / 2.5% (2nd)
Copper / 95.2% (1st) / 97.5% (2nd)
Fine Silver / 40% (1st) / 30% (2nd) / 23% (3rd) / 5% (4th) / 3% (5th)
Copper / 60% (1st) / 70% (2nd) / 77% (3rd) / 95% (4th) / 97% (5th)
Fine Silver / 60%
Copper / 40%
Shakudo / 83.3% (1st) / 71.4% (2nd) / 58.8% (3rd)
Shibuichi / 16.7% (1st) / 28.6% (2nd) / 41.2% (3rd)
Metal Arsenic / 1% (1st)
Copper / 99% (1st)
The dimensions of the materials are dependent upon the needs of the craftsman in terms of pattern, size, and thickness of the sheets. Estimates of potential relationships between the starting dimensions and finished dimensions are listed:
Example / Width / Length / Thickness / No. of Layers
A / 5cm / 5cm / 1.6mm / 10
B / 7.5cm / 7.5cm / 1.6mm / 13
C / 10cm / 10cm / 1.6mm 20
AFTER DIFFUSION-FORGED & PATTERNED:
Example / Width / Length / Thickness
A / 11.5cm / 11.5cm / 1.6mm
B / 20cm / 20cm / 1.6mm
C / 37cm / 37cm / 1.6mm
After selecting more than two different nonferrous materials to be used, their thickness and size, the numbers of layers, and the sequence to be stacked, cut into the desired shape: square, round or rectangular. Remove any burrs that may be found on the edge of each sheet with a rough file. The sheets should be annealed, flattened, and pickled. With silicon carbide or any abrasive paper or cloth, abrade away heavy oxidation or dip in a solution of equal amounts of nitric acid and water and rinse well in water. Use fine pumice powder with a scouring pad or any other substance to degrease all the surfaces. Stack the sheets in the sequence selected handling carefully to avoid reintroduction of grease.
Prepare two mild steel sheets, approximately 6mm in thickness, to act as torque or pressure elements. Cut them at least one inch larger in each direction than the laminates and drill in the assembly. If the steel plates are new, paint with typewriter correction fluid or yellow ochre, as the steel plates might stick to the nonferrous metals during diffusion. The plates act as a weight, providing pressure, and as a heat sink. Assemble the torque plates, layers of metals and/or alloys with nuts and bolts as evenly and as tightly as possible.
If silver or silver alloys are used they should be placed in a steel box. The steel box will maintain a more even heat distribution and will keep the layers from sliding when sweating or diffusion occurs. A mild steel box of about 1mm to about .8mm in thickness is made to contain the silver laminates. The bottom dimension of the box should be the same size as the laminates; the height should be a little less than the total height of the stack for a maximum amount of pressure to be applied. The steel box should have a window, or opening on at least one side, so that the heat generated colors can be observed while diffusing. It is suggested to insert silver in between every layer of the remaining laminates, because of the silver's lower melting point as compared to copper, Kuromi-do or Shakudo.
The diffusion is done in the blacksmithing forge using metallurgical coke for its capacity to produce sufficient heat and reduction atmosphere. Build three side walls with standard fire brick. Place a sheet of steel on top of the fire brick walls to act as a roof to contain the fire more efficiently. Ignite the coke and allow to burn halfway through or more. When there exists a strong fire, and it encompasses the entire cavity produced by the side walls, insert the assembly into the fire. The flame should now be producing a reduction atmosphere which is conducive for diffusion. Heat soak for about 10 to 20 minutes, dependent upon the mass; i.e., 20 layers of 10cm x 10cm x 1.6mm will take about 10 minutes to diffuse. It is a good idea to turn the assembly over a couple of times in the forge during diffusion, when the bottom of the assembly turns red for even distribution of heat. This is to be done in the flames of the fire to avoid oxidation of the metal. When the laminates turn red-orange, rotate the assembly frequently as it will soon begin to sweat. When the color of the entire assembly is almost bright orange, take out from the forge and cut the nuts and bolts off quickly with a cold chisel. When the billet is still red, hot forge from the outer edge to the center to avoid splitting.
When dealing with silver as a laminate, one should watch the silver only during diffusion. The timing is about the same as for copper and copper alloys. It is a good idea to place the assembly level in the forge, in case it begins to melt. When silver sweats, stop heating immediately and remove from the forge slowly, keeping the assembly level, and place on an anvil to cool and solidify. Proceed to cut off the nuts and bolts. Remove the billet from the steel box and forge when the silver contained diffusion is at black heat; the heat at which all the red heat has dissipated. Do not hot forge at red heat a silver contained billet, it could result in the cracking of the entire billet. After the laminates have been successfully diffused, trim all the sides with a hacksaw or power bandsaw. Cracking could occur in subsequent forging because of possible oxidation at the edges and uneven stacking.
After diffusion and trimming of the edges, reduce by forging to desired thickness for appropriate pattern; 7mm to 5mm is recommended.
There are a number of procedures to develop and control patterns. Traditionally, the pattern is produced by using the Hatsuri-Tagane, which is a cutting chisel shaped like a wood gouge or a Maru Tagane, both produce a similar cut: a U-shaped channel. Put the diffused metals into a pitch block, pitch bowl, or large machinist vise. Carve through at least three layers. Remove from the holding device. Forge out until almost completely flat. Repeat the sequence of carving and forging at least four times observing the resultant pattern emerging. Continue forging until desired thickness needed. It is now ready to be raised or formed. Surface patterns on holloware can be created with the use of chisels. A metal drill bit may be used to develop a pattern, but it is necessary to use a round headed burr to smooth the bottom and top edge of each drilled hole because of the high angle of the drill's contour and point. If this is not done, folding of the top edge of the drilled hole will cause small cracks to appear in the pattern. Chiseling and drilling can be combined to produce patterns. A milling machine can be used to develop patterns. The use of a two fluted ball and mill can achieve similar results as the Hatsuri-Tagane. The object in patterning is to find a tool that will remove metal and produce smooth, long-angled, u-shaped channels or holes.
The diffused laminae can be treated as any single piece of metal. Patterns can be developed without tools that remove metal. The preparation and the procedures of diffusion are the same, except the shape of the laminates are rectangular or sliced to produce a bar from a large billet. After diffusion, forging on edge will result in a stripped pattern throughout. A variation of pattern development by edge or side forging and grinding can be accomplished. Before forging is started, the billet can be partially ground at right and/or oblique angles to the edges of the billet to partially destroy the parallelness. The edge forged pattern will remain the same on both sides and produce parallel strips that are distorted or wavy by the action of forging.
Blacksmithing techniques can be utilized for another type of pattern. Heat the bar or rectangular billet to red-orange if copper and copper alloys are present, and quickly place in a vise. While still red, twist with a wrench or similar tool. Repeat until desired twists are attained. While twisting, folding of the edges may occur along the outside of the twist. This should be removed by filing. Hot forge and draw out to rectangular bar form. The pattern of the simple twist can be sliced horizontally to create a pattern of great potential, the star or core of the twist. Another bar could also be partially twisted and hot split, forged and finished. Two other bars can be twisted, one to the right and one to the left, both rediffused and twisted again to produce a simple, elegant sculptural form.
Patterning has very few limitations. Those are of the manipulator. Patterns can be mathematically or geometrically conceptualized, but variables both planned and accidental occur that the manipulator must seize and take advantage of to produce a pattern that is other than mundane. Patterns can be etched to create a relief surface much like drift wood. The acids will react or attack the metals and alloys, in the billet, at different rates producing a tactile, relief surface pattern. Acidic solutions to etch and produce subtle colorations were used in Damascus Steel, Wootz Metal, true wrought iron, and of course the Japanese sword blade to emphasize the patterning produced during or after forge welding. The coloring is very important to emphasize patterning in Mokume-Gane. In Japan, a commercially available patina called Rokusho is used. Rokusho is an etchant and creates different oxidizes on the surface of the metals laminated. A Mokume-Gane patterned sheet before coloring shows little of the inherent pattern, but after being colored in Rokusho, the results are often spectacular. The final step in the process is to coat the surfaces with a protective film, such as wax.
Kuromi-do contains either 99% copper and 1% metallic arsenic or 97% copper and the remaining 3% a combination of iron, nickel, lead, arsenic, antimony, sulfur, aluminum, and phosphorus. Since it contains metallic arsenic, please wear a mask while filing and sanding. Annealing must be done under good ventilation, and wash hands thoroughly after using. We are not responsible for any accident caused by Kuromi-do or Rokusho.
Coloring of Kuromi-do
Boiling in a solution of Rokusho (Japanese patina compound) will give to Kuromi-do a blackish color. Mix the solution in a copper pan or Corning ware. Do not use stainless, aluminum, steel, brass, bronze, or enameled steel pans. Bring to a boil the following ingredients: Rokusho, 4 grams; copper sulfate, 4 grams; and distilled water, 1.8ml. Work under good ventilation.
1. Finish all forming, soldering, etc. Coloring is the last process in finishing a piece of metal work.
2. Remove all firescale before the piece is to be colored. Boil the piece in water to remove any surface grease and oils if it has been buffed. Or use a commercially available cleaner. Fantastik is a good grease remover. Clean in a strong pickle solution.
3. Cover the object with ground Daiken Japanese radish) if pieces contain silver and then dip into the boiling solution, keeping the piece constantly moving, for ten minutes. Remove from the solution and immediately immerse in a nearby container of water to avoid water spotting or particles of Rokusho drying on the surface of the piece.
4. Repeat step 3 several times until the coloration is achieved. It usually takes 30 minutes to one hour.
5. After coloration, coat with Renaissance Wax and buff with a soft cloth. Lacquer can also be used as a protective coating.
Kuromido and Rokusho
Shakudo, Shibuichi, Rokusho, Tools
25% Shibuichi, 26 layers in brass/copper and silver/copper flat,
straight and ladder patterns, and ready made Mokume-Gane
© Hiroko Sato Pijanowski & Gene Michael Pijanowski, School of Art, The University of Michigan, 2000 Bonisteel Blvd., Ann Arbor, Ml 48109, Tel/Fax: 313/769-1762