Optoelectronics engineers have discovered how to make gold of any colour by carving tiny shapes onto its surface. Then we may have some stickers directly printed on the metal surface.
Gold absorbs blue light and this produces its characteristic yellow colour. And copper absorbs blue and green light making it look a reddy orange.Other colours are hard to come by without coating the metal or carving a diffraction grating onto its surface to produce a characteristic interference pattern, like those from a compact disc.
But now there’s another way thanks to some interesting work by Jianfa Zhang at the University of Southampton and a few pals. Their idea is to carve a different type of repeating pattern on to the surface of a metal.
These patterns are smaller than the wavelength of visible light. Instead of causing the light to interfere, they work by changing the properties of the sea of electrons in the metal–in particular its resonant frequency. This alters the frequency of light it absorbs and reflects.