Physicists at the University of Southampton have announced a
surface patterning technique that allows metals such as gold,
silver and aluminium to be perceived as different colours.
Using ion beam milling (a technique the announcement describes
as "sand-blasting on the atomic scale") the team are able to make
precise changes to the surface pattern of the metals which affect
how light is reflected. These changes in how light interacts with
the metal lead can be used to cause the human eye to perceive the
material as being of a different colour.
"This is the first time the visible colour of metal has been
changed in this way," says professor Nikolay
Zheludev, a specialist in nanophotonics 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."
The small size of the patterns (just 100 nanometres across) is
the key to their colour changing ability -- for the phenomenon to
be successful each of the individual parts of the pattern must be
smaller than the wavelength of the incidental light.
The announcement of the nano-patterning technique offers an
alternative method for colouring metals to that unveiled earlier in
October by Harvard's School of Engineering and Applied
Instead of making changes directly to the source,
the Harvard option uses a germanium layer to change the way
light refracts when it comes into contact with the metal.