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Gold – soon to be available in colors other than gold

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October 24, 2012

Scientists have developed a new process for changing the surface color of gold and other m...

Scientists have developed a new process for changing the surface color of gold and other metals (Image: Shutterstock)

Although a great many people like the “prestige” that comes with the natural color of their gold jewelry, teeth or vacuum cleaners, things are about to get a little more complicated – scientists from the University of Southampton have now devised a technique that causes gold (or other metals) to be seen in a variety of other colors ... green gold, anyone?

Unlike processes such as anodizing, in which colored films are added to metal surfaces, the Southampton technology works by actually altering the gold itself. Tiny raised or indented patterns are embossed onto its surface, changing the way that it absorbs and reflects light. Depending on the shape, height and/or depth of the pattern, that reflected light can be seen as any one of a number of colors. Different patterns could even be applied to the same object, causing different parts of it to take on different colors.

“This is the first time the visible color of metal has been changed in this way,” said project leader Prof. Nikolay Zheludev. “The colors of the objects we see all around us are determined by the way light interacts with those objects. For instance, an object that reflects red light but absorbs other wavelengths will appear red to the human eye.”

Other metals, such as silver and aluminum, can also be “colorized” using the technique. Along with its obvious applications in fields like jewelry-making, it has been suggested that the technology could additionally find use in making items such as banknotes harder to forge.

The patterns are presently being applied using an existing technique known as ion beam milling, which is described as being similar to sand-blasting on the atomic scale. However, the scientists believe that industrial-scale processing would be possible via methods such as nano-imprint, in which a master template is used to stamp out patterns on surfaces.

The university has filed for a patent on the technology, and is looking into its commercialization.

Source: University of Southampton

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
12 Comments

That's not gold, It's Kryptonite! RUN SUPERMAN RUN!!!

Derek Howe
24th October, 2012 @ 03:55 pm PDT

Now, look, I don't mean to be pedantic or anything, but the color of gold... is gold. That's why it's called gold. What YOU have discovered, if it has a name, is some...Green.

Stratosfire
25th October, 2012 @ 04:18 am PDT

Aluminum anodyzing is not a film. It is a porous, but thickened layer of aluminum oxide (sapphire) with a penetrating dye if color is wanted.

Bob Stuart
25th October, 2012 @ 08:24 am PDT

And now the team is working on how to make diamonds look like glass.

8^)

warren52nz
25th October, 2012 @ 01:44 pm PDT

Careful Bob. Anodize isn't saphhire but a hydrated oxide of aluminum. We denote sapphire and ruby as different gems though they are single crystals of aluminum oxide with different impurities to give color.

Gold can also look green if it's very very thin. Noticed this when gold coating electron microscope samples years back. Maybe some optics expert/nano expert can comment on that. Have to wonder if each metal has it's own characteristic color palette available.

joez
25th October, 2012 @ 01:45 pm PDT

An interference filter...big woop.

Besides, just TRY and give her a GREEN ring, ya boffins

solutions4circuits
25th October, 2012 @ 02:07 pm PDT

NOVA Science Now just had a show on this tonight, making things smaller. It explained why gold makes red glass.

Nanoparticles. Get particles of gold small enough and they don't reflect yellow light but still reflect red light.

Alter the surface structure of gold just right and the spectrum of light it reflects best is altered.

The problem with a technique like this on a soft metal is it won't be damage resistant. Dents and scratches will obliterate the micro patterns and reflect the natural yellow color of gold.

Canada's mint already used a process like this to impress holograms onto the surface of .9999 fine gold coins. Regular .999 fine gold wasn't soft enough. Don't touch them, the oil from your fingers could fill in the micro patterns. Getting them clean without wrecking the hologram, not easy.

Gregg Eshelman
26th October, 2012 @ 12:51 am PDT

This is just palin stupid. This is first of all a "technology" well known from nature. Butterflies wings appear colored due to sub-wavelength patterns. People have also utilized that by molding metals from actual butterfly wings.

And it has been done by nano lithography without the use of actual butterfly wings.

One applicaion close to commercial use is the black silicon used to enhance efficiency of solar cells. In that case silicon is patterned with sub-wavelength patterns to reduce reflections to a minimum. And due to that the otherways metallic silvery look of silicon becomes black since it is reflecting a minimum amount of light.

So good luck with that patent.... unless it is a patent for the method of producing this for commercial applications.

D-man
26th October, 2012 @ 02:55 am PDT

Oxide layers can be used to create colour in many metals. The technique above could make coins hard to replicate, but would require some protection against wear, and would have to be easy to distinguish from other cheaper techniques that could be used for forgery.

Charles Bosse
26th October, 2012 @ 10:39 am PDT

Gold doesn't oxidize, which is one of the reason's it has been a prized metal for thousands of years.

Gregg Eshelman
30th October, 2012 @ 07:59 pm PDT

Sub-wavelength patterns in gold are more durable than butterfly wings, but still soft. A bump will flatten the pattern and change the color.

SuperFool
17th April, 2014 @ 11:24 pm PDT

There’s a university in Rochester that developed a way to blacken metal using a laser, sounds similar.

William Carr
21st April, 2014 @ 04:52 pm PDT
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