This is a traditional Japanese technique of diffusion welding precious
and nonferrous metals. The result is a Damascene-like composite which can
produce all the patterns known from pattern-welded steel, such as random
or controlled layered patterns or torsion patterns. Mokume Gane is much
more sensitive to internal stresses than layered steel, resulting
in cracks especially on the edges.
Mokume Gane, literally translated Wood-Gained-Metal, has been developed
by Denbei Shoami (1651 - 1728) in ancient Japan. Shoami is actually the
highest title given by the Shoam-School, one of the 5 Japanese Sword Schools.
The privilege of using this title proves the outstanding talents of Denbei
Shoami who has created remarkable artifacts in many fields of arts and crafts.
Bowl of Mokume Gane (K. Loose) | Mokume Gane has often been used for hilts and tsubas but was also used for precious metal containers and other artifacts. Today Mokume Gane is a soughtafter material for jewelry, and is being used by some artists for knife-handles and other objects. |
It is not possible to diffusion weld nonferrous metals by hammer since
they cannot be easily freed from their oxide-skin by fluxes. It is necessary
to heat oxide-free layers under high pressure to receive a proper diffusion
weld.
The sheetmetal pieces have to be freed from grease, oxides and dirt
when preparing to weld a Mokume Gane. Scotch Brite with soapy water is
suited for this work. The sheet metal pieces are air-dried thereafter and
may not be touched by bare hands.
The cleaned sheets are stacked according to the desired order. Caution
has to be taken not to stack 2 sheets of the same metal upon each other,
since this will cause a weak bond. The whole package is then placed into
the "press" after being wrapped into a singe layer of paper to prevent
it from sticking to the press. This press is made from 2 thick steel plates
with several heavy screws, ideally from high temperature steel. High
temperature grease should be used to prevent the screws from getting stuck.
By tightening the screws, the packet of Mokume Gane is pressed. The whole
is then placed into the fire furnace.
The combination of high pressure and temperature causes a diffusion weld
between the sheets of metal. The lowest eutectic melting point of all present
metal combinations limits the maximum permissible temperature. The temperature
actually applied should stay about 10° to 20°F below the eutectic
melting temperature which is always below the melting temperature of the
metals used. When the eutectic melting temperature is reached small droplets
of liquid metal are observed on the edges of the Mokume Gane packet.
It looks as if the metal is sweating. Further heating will result in melting
the entire packet.
When using more than 2 different metals, it is helpful if the eutectic
melting point of all present combinations is located in a similar range.
This way all bonds will have similar strength.
By hard-soldering sheet metal, a compound similar to Mokume Gane is produced. The bond is produced by solder flowing, driven by capillary action, into the spaces between the layers. This generally causes wider alloyed zones, characterized by distinctly different mechanical properties. Often the solder is more brittle than the adjacent metals. It is hard to impossible to twist Mokum Gane produced by cheating techniques.
Mokume Gane should be forged in the range between room temperature
and black heat (when no heat color is visible). While forging the work, hardening is felt very pronounced; heating to dull red will soften the metal again. Special caution has to be taken while controlling
the pattern. |
Rings made of Mokume Gane |
© 2005 G.v.Tardy
