What is Dichroic Glass?

I've heard it called all kinds of things.... Dichronic, dichromic, or even diachromatic glass. So, just what is this stuff folks just can't seem to remember the name of?

The beginnings of dichroic glass go back to the 1960's when NASA began development of this material for use as optical camera filters and cosmic radiation shields. It is still used  by the space program today.  One example you have probably already seen is the golden sheen on an astronaut's face shield.  This is a dichroic coating meant to protect against unfiltered sunlight while they are working in space.

The wonderful, varied colors that you see in dichroic glass are not created through the use of paints, dyes, any standard coloring agent.  Those glorious colors are created through the manipulation of light. The multi-colored effect is the result of complex light interactions called "thin film physics". Thin-film physics also give us the rainbow colors in a soap bubble, and the beautiful reflections and shimmers in a peacock and dragonfly wing.

Dichroic glass is created by vaporizing various metallic oxides (like silicon,titanium, and magnesium, just to name a few) along with quartz crystal in a vacuum chamber.  The vapor molecules are then deposited onto the surface of a sheet of pristinely clean black or clear glass.  Varying amounts of time and temperature determine the thickness of the oxide deposited on the glass.  The total thickness of the oxide layers totals no more than 35 millionths of an inch! Believe it or not, a human hair is about1000 times thicker.

The metallic oxides in the dichroic coating cause different wavelengths of light to either reflect or transmit more than others. This causes certain light waves to be reflected while others travel through the glass along slightly different paths causing the color shift.  Most dichroic glass uses both transmission and reflection of light to achieve the desired effect so that as you rotate a piece of dichroic glass, even slightly, you'll see shifting rainbow of colors. The physical properties that determine the final effect include the type of oxide,the number of different oxides used, the order, number and thickness of layers,and the pattern (like hearts, dots, squares, etc.). With so many variables,dichroic glass presents an incredibly rich and varied palette of colors and patterns to work with.