Anyone, Just wondering about opal again. I have heard many times of
the fact that opal colors stem from destructive interference from
the orderly array of hydrated silica spheres and voids like
diffraction grating. Now, what of the very high quality opals that
seem to “glow in the dark” with color? You know, the intense red
flash in a room with only one candle and otherwise total darkness?
Is it simply that our pupils have dialated to accomodate the
darkness? If the opal uses destructive interference or simple
diffraction, you cannot have more light photons exiting the stone
than entering at a given wavelength. Could it be that the silica
spheres are actually stacked not precisely in a plane, but rather
some slight parabolic shape that could in some way concentrate a
larger area of a given photon density into a higher photon density
but a smaller cross section?