In this article, Nature says that "tiny metal particles give 15th century Italian ceramics lustre." Here are some details.
Artisans throwing pots in fifteenth- and sixteenth-century Umbria were practising an early form of nanotechnology, Italian researchers have found.
Coloured glazes in pottery samples from the Umbrian town of Deruta exploit the reflective properties of minute metal grains to give them a rich lustre, Bruno Brunetti of the University of Perugia and colleagues find.
Among the most striking Deruta ceramics are those with iridescent or metallic glazes. Some look like gold, others are iridescent -- changing colour when viewed from different perspectives.
Particles of metal of between 5 and 100 billionths of a metre across -- technically, a nanomaterial -- underlie this effect. Brunetti and colleagues found last year that red-and gold-lustre glazes contain particles of copper and silver, respectively, in this size range. Instead of scattering light, the particles' minute size causes light to bounce off their surface at different wavelengths, giving metallic or iridescent effects.
And the story becomes even more interesting. Nanotechnology meets alchemy!
Historical evidence for the early nanotechnology survives in the potter's handbook of around 1557, Li tre libri dell'arte del vasaio, by Italian craftsman Cipriano Piccolpasso. Copper and silver salts were mixed with vinegar, ochre (iron oxide) and clay and applied to the surface of pottery already coated with a glaze. A delicately regulated firing technique resulted in a pot with a lustrous surface.
In the Renaissance, these effects, which today would be seen as merely pleasing, had a deeper significance. Turning mundane materials into something resembling gold was regarded as a feat bordering on alchemy. The ability to change colour was regarded as an alchemical property, making iridescence magic too.
For more information, you can read the abstract of this research paper, "Copper in glazes of Renaissance luster pottery: Nanoparticles, ions, and local environment," published by the Journal of Applied Physics.
Source: Philip Ball, Nature, June 30, 2003
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