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Sure, we have rose gold, white gold, and well, gold gold, but what if you could have red, blue, green, or even purple gold without chemically altering the precious metal? Researchers at the University of Southampton in the United Kingdom opened up a spectrum’s worth of possibilities when they discovered they could change the way gold—or just about any metal—reflects and absorbs light. The secret involves a bit of visual sleight of hand. By etching the metal’s surface with patterns of specific shape and depth, Nikolay Zheludev and his team at Southampton’s Optoelectronics Research Centre are able to manipulate the wavelengths that are visible to the human eye.
Color is determined by the way light interacts with different objects. A red apple, for instance, appears red because it reflects red light but absorbs all other wavelengths. “This is the fundamental principle we have exploited in this project,” Zheludev, who led the project, says. “By embossing metals with patterns only around 100 nanometers across, we’ve found that we can control which wavelengths of light the metal absorbs and which it reflects.”
A red apple appears red to the human eye because it reflects red light but absorbs all other wavelengths.
The “nano-patterning” is carried out using established processes such as ion-beam milling, which is similar to sandblasting, albeit on an atomic level.
The discovery, according to Zheludev, could deliver valuable economic and environmental benefits. Not only could the technique be harnessed to manufacture jewelry but it could also make banknotes and documents more difficult to forge. It could even be used to create a wide range of colors on a given metal, imbuing it with sophisticated optical properties that are almost impossible to imitate.
“We’ve filed a patent application to cover our work,” Zheludev says, “and we’re currently talking to a number of organizations about taking our breakthrough towards commercialization.”