It sounds sort of like alchemy, but scientists from the University of Rochester have used the latest technology to turn any metal just about any color.
(From left) Gold aluminum, blue titanium, and gold platinum.: Credit: Richard Baker, University of Rochester
Researcher Chunlei Guo and his assistant Anatoliy Vorobeyv shine a very intense laser pulse at a metal for a fraction of a second. More precisely, they unleash as much power as the entire electric grid of North America, focused onto a point smaller than the dot on the letter "i." Nevertheless, the laser can still be powered by a regular wall outlet. The laser intensity changes the surface of the metal, forming tiny structures that reflect certain wavelengths of light, determining the color of the metal.
The scientists can also control how this "femtosecond laser" forms the metals, in order to make the surfaces respond to incoming light in different ways. By varying the laser intensity, pulse length, and number of pulses, the researchers can control the etching and therefore control the color. Further, they can etch the metals in such a way as to cause reflected light to interfere differently in different directions. This makes the metal appear different colors depending on the angle it's viewed at, making it iridescent.
The technique works on every metal the researchers have tried. These include aluminum, platinum, titanium, tungsten, silver, and gold - all of which can be colored blue, purple, gold, and other colors. Although it currently takes about 30 minutes to etch a surface about the size of a dime, the researchers believe they can speed it up for practical purposes.
Guo has been famous for working on changing the colors of metals since 2006, when he demonstrated a method to create a black metal that absorbed virtually all visible light.
via: University of Rochester