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Color-changing Gold

Gold that comes in various colors is not a new concept. Just like mixing colors of paint, gold will change color once other metals or impurities are alloyed with it. But, thanks to scientists at Southampton University, that type of gold coloring may be a thing of the past.

Thanks to a new type of nanotechnology, it’s now possible to turn a piece of gold into nearly any other color without chemical treatments, coatings, or alloying. The key to this new coloring process is to understand why objects have their natural color.

Color is determined by how an object reacts with light. The amount of light that is absorbed or reflected by an object determines that object’s color. Scientists have found that by embossing gold a certain way, they can change how the gold reflects light – and thus, change its color entirely. The embossing pattern is made up of channels so small they are imperceptible to the human eye – about 100 nanometers. For reference, that’s about 1/400th the width of a strand of hair. The individual features of the embossed pattern are actually smaller than the wavelength of certain incidences of light, causing them to reflect back and changing the color of the gold.

Real-world applications are varied. Using this technique has infinite design possibilities for the world of jewelry. Jewelers could create gold rings with swirling red, yellow, green, or any other colors. The embossing technique can be applied to silver and other metals as well, so the possibilities really are endless.

This new embossing method could also be used as a security feature to prevent forgeries or counterfeiting. Metals are embossed using an ion beam milling machine (think etching or sandblasting at an atomic level). Unless a counterfeiter is a super-scientist with a multi-million dollar budget, he or she is not going to be forging anything.

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