Experts change the colour of gold

British scientists have managed to upstage King Midas by changing the colour of gold.

While the mythical king turned everything he touched to gold, the researchers transformed the precious metal by altering the way it absorbs or reflects light.

So gold no longer has to be golden - it can be red or green, or a multitude of other hues.

The technique involves embossing tiny raised or indented patterns onto the metal's surface.

It can also be applied to other metals, such as silver and aluminium, and opens the way to colouring metal without coatings or chemically treatments.

Applications may include anything from manufacturing jewellery to making banknotes and documents harder to forge, say the scientists.

Professor Nikolay Zheludev, who leads the University of Southampton team, said: "This is the first time the visible colour of metal has been changed in this way.

"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."

Details of the research have been published in the journals Optics Express and the Journal of Optics.