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Researchers at the University of Southampton have developed a new way to alter the color of gold—or just about any metal— without chemically altering it. The technique involves “nano-patterning” — etching the metal’s surface with patterns of specific shape and depth, which manipulates the wavelengths that are visible to the human eye. The technique could deliver valuable economic and environmental benefits, and it could be harnessed to manufacture jewelry and to make banknotes and documents more difficult to forge.