November 14, 2017
Opalized glass or opalite is a remarkable material that exhibits beautiful colors when exposed to sunlight, but its truly special nature is revealed when illuminated by a white spotlight in a darkened room, as shown above. Here, a 1.25 in (3 cm) long, egg-shaped piece of opalite is being illuminated, from the right, by a white LED lamp. A significant fraction of the light is scattered in every direction, making the glass piece visible for the camera. The non-scattered part goes through the opalite and illuminates the white paper, at left.
The colors result primarily from Rayleigh scattering; the same phenomenon responsible for the blue color of the sky -- light is scattered by air molecules that are much smaller than the wavelength of the light. As the LED light passes through more of the opalite the shorter wavelength blue light is scattered out, producing the green and yellow colors. As light propagates through more and more of the opalite, finally only the longer wavelength red colors remain. In essence, the opalite scatters the LED light in the same way our atmosphere scatters sunlight as the Sun approaches the horizon during sunset.
Photo Details: Nikon D5200 camera; 1/3 sec. exposure; : f/5.6; ISO 100; 55 mm; RAW image processed with UFRaw; color temperature of 5780 K converted to sRGB.