Beyond Gold and Platinum: Mokume Gane
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.