Gold is now available in colors besides gold

Gold is more than a metal. It's a symbol, the physical incarnation of value and wealth and luxury, and this has been the case for thousands of years. This is partly because gold can be readily found and is easy to work, but also because of the appeal of the color and shine. So what's going to happen now that gold can be made into any color? Anarchy, that's what.

For better or worse, we're not talking about some sort of inverse Philosopher's Stone here: the gold in question is still gold, in that it's made up entirely of gold atoms. What scientists boffins from Southampton University have figured out how to do is to alter the surface of the gold to make it appear as though it has any color under the sun.

Color, remember, is just the way that light interacts with an object. In any given material, some wavelengths of light are reflected, and some are absorbed. Whatever is reflected is what we see, and that's where color comes from: if something absorbs all colors except red, for example, we see it as red. What colors get absorbed and reflected is a property that's usually inherent in the composition of a material (as with most pigments), but it's also something that can be controlled by the structure of a material. Remember those berries from last month? Their color comes from nanoscale features that control which wavelengths of light get scattered and which ones get reflected. The Mirasol display uses the same sort of trick.

So anyway, these scientists boffins have come up with a way of etching nanoscale features into the surface of gold using an ion beam, and by changing the height, depth, and pattern, they can cause gold to reflect any color you want, from orange to green to red to purple. This technique isn't just about gold, either: it works on any metal, and by combining different patterns, you can create finely detailed multicolored designs, effectively turning the surface of your bit of gold into a metamaterial:


One interesting question here is just how much gold is worth if it's not, you know, gold. Gold alloys of different colors (like white gold or rose gold) are fairly common, and there are actually lots of other colors that you can get by mixing pure gold with different metals, including red, blue, black (oxidized), and purple. These aren't just tints, either: the pics below show 18 carat purple and blue jewelry, using alloys of aluminum and iron.


The difference with this new method, though, is that there's no alloying involved: it's pure, 24 carat gold, no matter what the color. And if you scratch the surface, you'll find the original color within. The Southampton researchers have patented the process of changing the color of gold, and they say that they're trying to market it for commercial jewelry making.

Southampton, via BBC

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