Another nanotechnology has been around for centuries. It is the use of nanoscale impurities to affect the color of glass. Just as today's well-understood gold nanosphere suspensions provide color indicators for a variety of purposes, medieval stained-glass relied on the same size-dependent light scattering properties of metal nanoparticles.

Gold and silver salts were used in medieval times to color glass used in church wndows. For example, silver particles were used to stain glass yellow, while gold particles were used to stain glass red. The aggregation of metal into nanoparticles with surface-plasmon resonances which variously affected their spectral transmissivity is ony today's 20-20 hindsight analysis of archaic technology.




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