A new take on the Midas touch: Changing the colour of gold

Oct 24, 2012
A new take on the Midas touch - changing the colour of gold
The tiny patterns are formed on the gold surface using a process called ion beam milling (the focused ion beam system is used to create nanoscale intaglio metamaterial patterns on the metal surface.

Red gold, green gold – a ground-breaking initiative has found a way of changing the colour of the world's most iconic precious metal.

A University of Southampton team have discovered that by embossing tiny raised or indented patterns onto the 's surface they can change the way it absorbs and reflects light – ensuring our eyes don't see it as 'golden' in colour at all.

The finding results from a major initiative funded by the Engineering and Physical Sciences Research Council (EPSRC) targeting the development of a new generation of nanotechnology-enabled materials.

Equally applicable to other metals such as silver and aluminium, this breakthrough opens up the prospect of colouring metals without having to coat or chemically treat them. This could deliver valuable economic, environmental and other benefits.

The technique could be harnessed in a wide range of industries for anything from manufacturing jewellery to making and documents harder to forge.

"This is the first time the visible colour of metal has been changed in this way," says Professor Nikolay Zheludev, Deputy Director of Southampton's Optoelectronics Research Centre, who led the project.

"The colours of the objects we see all around us are determined by the way light interacts with those objects. For instance, an object that reflects but absorbs other wavelengths will appear red to the .

"This is the fundamental principle we have exploited in this project. By embossing metals with patterns only around 100 nanometres across, we've found that we can control which the metal absorbs and which it reflects." * 

The precise shape and height or depth of the patterns determine exactly how light behaves when it strikes the metal and therefore what colour is created. The technique can be used to produce a wide range of colours on a given metal.

A silver ring, for example, could be decorated with a number of different patterns, making one part of it appear red, another part green and so on; metal features with sophisticated optical properties that would be almost impossible to imitate could be incorporated into documents as security features. 

The nano-patterning is carried out at the research level using well-established techniques such as ion beam milling, which may be envisaged as sand-blasting on the atomic scale.

However, the concept may be scaled for industrial production using such processes as nano-imprint, whereby large areas are stamped out from a master template in a manner comparable to CD/DVD production. 

"We've filed a patent application to cover our work," Professor Zheludev says, "and we're currently talking to a number of organisations about taking our breakthrough towards commercialisation."    

Explore further: Simpler process to grow germanium nanowires could improve lithium ion batteries

More information: J. Zhang, J. Y. Ou, N. Papasimakis, Y. Chen, K. F. MacDonald, and N. I. Zheludev, "Continuous metal plasmonic frequency selective surfaces" Optics Express 19, 23279 (2011) [doi: 10.1364/OE.19.023279]
J. Zhang, J. Y. Ou, K. F. MacDonald, and N. I. Zheludev, "Optical response of plasmonic relief meta-surfaces" Journal of Optics 14, 114002 (2012) [doi:10.1088/2040-8978/14/11/114002]
"Method and device for controlling the color of metals" (US patent application 13/182,084 (13/07/2011); GB application 1011720.8 (13/07/2010))

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Lurker2358
1 / 5 (1) Oct 24, 2012
This is the fundamental principle we have exploited in this project. By embossing metals with patterns only around 100 nanometres across, we've found that we can control which wavelengths of light the metal absorbs and which it reflects."


Blurs the boundary between the definitions of "physical change" and "chemical change" as per standard text book or encyclopedic definitions.

"We've filed a patent application to cover our work," Professor Zheludev says, "and we're currently talking to a number of organisations about taking our breakthrough towards commercialisation."


As I understand it, you can't patent a fundamental property of nature, which is a good thing.
bret_brickner
5 / 5 (1) Oct 24, 2012
this is a nice idea for an art project or visual stimulation but how about applying this concept to solar cells so that they can absorb more light at smaller/larger incident angles and intensities?
IronhorseA
not rated yet Oct 24, 2012
"metal features with sophisticated optical properties that would be almost impossible to imitate could be incorporated into documents as security features."

If it can be produced in the first place, then it can be reproduced, albeit with a great deal of expertise required on the part of the forger.
christ_jan
not rated yet Oct 24, 2012
Its all about the geometry!
Lurker2358
1 / 5 (1) Oct 24, 2012
The counterfeiting application is stupid.

All you need is a plastic coin with an RFID chip programmed with the coin's face value, it's face serial number, and a password. The password would be unique to each legal coin, and the coins could be in any denomination ranging from 1 cent to 1 dollar. It could not be counterfeited because each serial number is assigned to a single denomination and a single password which is different for every coin of that denomination. The automated currency system would track transactions so that a coin being involved in impossible transactions (such as A to B and C to D without going from B to C) would be detected as a counterfeit (unless B reports a gift to C).

This is so simple it's ridiculous, and literally impossible to counterfeit without immediately being caught, and because plastic and glass lasts for hundreds of years, the coins would be much more durable than existing paper bills, increasing their circulation life time, decreasing costs...
Silverhill
not rated yet Oct 24, 2012
"We've filed a patent application to cover our work," Professor Zheludev says, "and we're currently talking to a number of organisations about taking our breakthrough towards commercialisation."
As I understand it, you can't patent a fundamental property of nature, which is a good thing.
There is such thing as a design patent, though, that can cover a novel manufacturing process.
PPihkala
not rated yet Oct 26, 2012
Lurker: Traceable currency is something people would not want. It would ruin one's privacy. It might also create problems for private transactions: When people buy something from another private person, because that would/could break the owner chain tracking.