All That Glitters…. Might Be Aluminum

Dr. Chunlei Guo, associate professor of optics at the Institute of Optics at the University of Rochester, has managed something alchemists tried to do for centuries. He can turn virtually any metal to gold. Well, gold in color, that is. Or blue, or black or just about any color. It is a permanent change to the outer layer of the metal and will not chip, peel or fade.

And he does it with a tabletop laser.

All that glitters golden is not gold. It could be aluminum. Or tungsten. Or another metal of Chunlei Guo’s choosing.

In a feat of optical alchemy, Dr. Guo, a professor of optics at the University of Rochester, and Anatoliy Y. Vorobyev, a postdoctoral researcher, use ultrashort laser bursts to pockmark the surface of a metal in a way that is not perceptible to the touch — it still feels smooth to the finger — but that alters how the metal absorbs and reflects light.

The result is that pure aluminum looks like gold, and the appearance is literally skin deep.

“I cannot tell it’s not gold,” Dr. Guo said. “It looks very pretty.”

Dr. Guo and Dr. Vorobyev reported their findings in the journal Applied Physics Letters published online Thursday.

The golden aluminum follows work a little more than year ago where Drs. Guo and Vorobyev reported that they could make gold and other metals look black — indeed a black that is blacker than the usual black, sucking up almost all light that impinged upon it.

The laser bursts — each lasting only about 60 millionths of a billionth of a second — melt and vaporize metal atoms near the surface, which then reassemble in minuscule structures including pits, spheres and rods that are a fraction of a millionth of a meter in size.

Here's the press release from the U of R.  

Since the process changes the intrinsic surface properties of the metal itself and is not just a coating, the color won't fade or peel, says Guo, associate professor of optics at the Institute of Optics at the University of Rochester. He suggests the possibilities are endless—a cycle factory using a single laser to produce bicycles of different colors; etching a full-color photograph of a family into the refrigerator door; or proposing with a gold engagement ring that matches your fiancée's blue eyes.

"Since the discovery of the black metal we've been determined to get full control on getting metals to reflect only a certain color and absorb the rest, and now we finally can make a metal reflect almost any color we wish," says Guo. "When we first found the process that produced a gold color, we couldn't believe it. We worked in the lab until midnight trying to figure out what other colors we could make."

Guo and his assistant, Anatoliy Vorobeyv, use an incredibly brief but incredibly intense laser burst that changes the surface of a metal, forming nanoscale and microscale structures that selectively reflect a certain color to give the appearance of a specific color or combinations of colors.

This will be a big thing in the near future, I suspect. Dr. Guo has already been fielding calls from jewelers who are very interested in the possibility of varicolored gold. Other consumer goods will not be far behind, I'm sure. One can also be fairly certain that someone will turn lead into gold (color-wise) in the near future and try to pass it off as the real thing. So it would be a good idea to remember that this can be done.

Maybe they should change Dr. Guo's title. Professor of alchemy has a nice ring. Maybe in a cornflower blue shade.