Mokume-gane (木目金 Mokumegane?) sometimes spelled Mokume-game, although this appears to be an erroneous variant; is a mixed-metal laminate with distinctive layered patterns. Mokume gane translates closely to "wood grain metal" or "wood eye metal".
First made in 17th-century Japan, the mixed-metal was used only for sword fittings until the Meiji era, when the decline of the katana industry forced artisans to create purely decorative items instead. The inventor, Denbei Shoami (1651–1728), initially called his product guri bori for its simplest form's resemblance to 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 traditional components were relatively soft metallic elements and alloys (gold, copper, silver, shakudo, 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.
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.
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 the traditional 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.
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. Flux inclusions could be trapped or bubbles could form. Commonly, imperfections need to be cut out, and the metal re-soldered.
Solid-state bonding (modern)
The modernized process 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 pattern
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.
To color the shakudo and gold, submerse the piece in boiling rokusho, and hold there, agitating constantly, until it reaches the desired color. Rokusho colors shakudo a black-purple. The more gold is in the alloy, the more purple it turns.
Rokusho is produced in small batches in a traditional process and is somewhat difficult to acquire outside Japan. There are some proposed substitute formulas (see rokusho article.)
Traditionally a paste of ground daikon radish is also used to prepare the work for the patina. The paste is applied immediately before the piece is boiled in the rokusho to protect the surface against tarnish and uneven coloring.
|Wikimedia Commons has media related to Mokume-gane.|
- Midgett, Steve (2000). Mokume Gane A comprehensive study. earthshine press. ISBN 0-9651650-7-8.
- Pijanowski, H.S. and Pijanowski, G.M. (2001). Wood Grained Metal: Mokume-Gane. Retrieved 2007-01-26.
- Binnion, J. E. and Chaix, B. (2002). Old Process, New Technology: Modern Mokume Gane (PDF). Retrieved 2007-01-26.
Media related to Mokume-gane at Wikimedia Commons