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 metal'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 banknotes 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 red light but absorbs other wavelengths will appear red to the human eye.
"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." *
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
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