In many ways the “ultimate” noble metal that one might consider for jewelry isn’t gold or platinum but their slightly tan colored cousin iridium. With the possible exception of osmium (which is smelly and toxic) it’s the rarest non-radioactive element in the earth’s crust — several times more so than either gold or platinum. It’s even more chemically incorruptible than the other two, it’s heavier (17% denser than gold and 6% denser than platinum), and it’s much more scratch-resistant. There’s also the additional mystique that most if not all of the iridium we mine comes from meteorite impacts and is therefore extraterrestrial. Unfortunately no one has come up with a way to work with it economically, mainly due to its absurdly high melting point and its glassy brittleness. The first artisan to tame iridium will surely take the world by the tail.
But in the meantime there’s a metalworking specialty that’s just as interesting if not more so called mokume gane (mo-KOO-may GAH-nay) which involves bonding as many as thirty alternating layers of differently colored metals; twisting, stretching, or otherwise heavily deforming the resulting mass; and then carving it into rings and such that display a riotously swirling agate- or woodgrain-like surface. Japanese metalworker Denbei Shoami (1651-1728) invented mokume gane to make ornamental handles for samurai swords. Metals used include silver; gold and differing hues of it such as rose, white, and green; shakudo (an alloy of 96% copper and 4% gold that develops a blue-black patina); kuromi-do (copper with a smidgen of arsenic); shibuichi (a pink copper/silver alloy); and various alloys of titanium and tungsten that can involve iron, nickel and molybdenum. They sandwich these layers and heat them to a temperature, which chemists call a eutectic, that’s hot enough to cause the atoms to jostle and intermingle at the layer boundaries yet not so great as to melt the stack into an undifferentiated blob.
It’s unquestionably a high art and something not everyone can pull off. Currently the best known mokume gane master appears to be Norio Tamagawa, whose family has worked the field for nine generations. You can Google the term yourself to find some good sources, but one of the most visible and accomplished is clearly James Binnion at http://www.mokume-gane.com