Mokume-gane

[1] Mokume-gane fuses several layers of differently coloured precious metals together to form a sandwich of alloys called a "billet."

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.

[4] 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.

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.

[3] 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.

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.

This technique joined the metals, but is difficult to perfect, particularly on larger sheets, because flux inclusions can trapped or bubbles could form.

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.

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.