Mokume Gane: A Japanese term borrowed from metalsmithing. It means "wood grain metal" and refers to the growth rings in trees. Various colors of metals are laminated together, positive and negative spaces are cut out of the laminate and it is rolled through a rolling mill creating a pattern similar to annular growth rings in wood.

Definition used with Permission, from
The New Clay : Techniques and Approaches to Jewelry Making
by Nan Roche, Chris Roche (Photographer), Sue Roche (Illustrator), Seymour Bress (Editor)
Paperback - 144 pages Reprint edition (March 1992)
Flower Valley Press, Inc.; ISBN: 0962054348