Nanotechnology: from the fourth century A.D. to the Middle ages

Today there was an interesting Quantum science seminar by Ulrik L. Andersen (Technical University of Denmark) Quantum Plasmonics: Controlled Coupling of a Single Nitrogen-Vacancy Center to a Silver Nanowire.

A question came up about plasmons in gold  nano-particles and how the surface plasmon frequency is renormalised downwards (i.e. blue-shifted) compared to the frequency in the bulk. Gerard Milburn pointed out that this is illustrated by The Lycurgus Cup in the British Museum. Coincidentally, an article by Mark Stockman in this months Physics Today states:

The resonant properties of plasmonic metal nanoparticles are readily apparent to the naked eye because the excitations absorb and scatter light at optical frequencies. The most ancient example is the famous fourth-century CE Lycurgus cup from the British museum, whose glass looks green in reflected light but ruby red in transmitted light. Those colors are complementary, evidence that there is little optical loss inside the glass. Investigation has shown that the dichroic glass contains nanocrystals of a gold–silver alloy at a fraction of less than 1%.

Such colloidal suspensions of gold and silver have been widely used in stained glass since the Middle Ages. Transmission through a silver colloid yields yellow light and transmission through gold yields ruby red. The magnificent colored light from the stained glass of the Sainte Chapelle in Paris is assumed to be largely due to the nanoplasmonic resonances.

Unlike glass-staining metal ions such as iron, chromium, copper, and cobalt, metallic nanoparticles, which both absorb and scatter, transmit light with an intensity that strongly depends on the incident and viewing angles. The Sainte Chapelle dramatically exploits the effect: At sunset, the grazing-angle scattering of light by gold nanoparticles in the windows creates a pronounced red glow that appears to slowly move downward, while intensities of blue tints from ions of copper or cobalt remain the same. The artistic impression, probably intended, suggests a stream of blood slowly flowing downward. [See the photo below].

BTW: I can't see the stream of blood.