I hope this isn’t a repeat but it is VERY cool. I’m a little
surprised by ~his~ surprise that we would be interested in colouring
metal. Ummm… Heck yeah! But I am wondering how robust it is really.
Lasers Make Other Metals Look Like Gold
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
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
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.
By changing the length, strength and number of pulses, the
researchers found they could vary the resulting color.
In some cases, the change causes the structures to absorb a
range of colors so that they cannot be seen. But the colors that
are not absorbed are still reflected, and thus visible,
resulting in gold aluminum or dark blue tungsten.
In other cases, the laser pulses create a periodic array of
structures that cause the reflected light to interact and
interfere with itself, producing an iridescent, shimmering
rainbow much like some butterfly wings, Dr. Guo said.
Dr. Guo imagines a kaleidoscope of potential uses, from the
practical (a reflective filter) to the whimsical (etching the
family photograph onto a metal refrigerator door, for instance).
Another possibility is custom colors for bicycles or cars,
without the need for any paint.
“It’s pretty robust, because it’s right on the metal, and it’s
not going to peel off,” Dr. Guo said.
He cannot yet make all metals into all colors but says he
believes that it is only a matter of trial-and-error to find the
right recipe for each permutation.
With his black metal finding, Dr. Guo suggested the possibility
of black gold rings. He was surprised when jewelers started
calling. “They are actually indeed interested in making colored
jewelry,” he said.
In the new article, he suggests a blue gold ring, perhaps a blue
to match the eyes of a fiance.