"Dichroic Glass" is somewhat of a misnomer, since the dielectric coating that produces all the interesting colors is not glass at all, but a group of very thin layers of metal oxides. This stack of thin layers has a total thickness of three to five millionths of an inch. The layers produce an "interference filter", creating the varied and unique color characteristics we see. Since the filter is so thin, it has very little mechanical integrity of its own, and must be supported on a mechanically stable substrate. Glass is the ideal candidate for this substrate. Transparent, rigid and stable, it withstands high temperatures, and is not affected by moisture, solvents or most acids. The filter materials are actually more chemically stable than most glasses used as the substrate. Thus, what we commonly call "Dichroic Glass", is actually a piece of dielectric interference filter attached to the surface of a piece of glass. 
 
Dichroic is defined as the property of having more than one color, especially when viewed from different angles. Dichroic glass is a high-tech spin-off of the space industry. Thin layers of metallic oxides, such as titanium, silicon, and magnesium are deposited upon the surface of the glass in a high temperature, vacuum furnace.

The glass to be coated is carefully cleaned, and fastened to a planetary arm in the top of the furnace chamber. The oxides are placed in a crucible on the bottom of the chamber. Air inside of the chamber is removed with a high vacuum-producing cyropump, and the chamber is heated to 300oF. The metallic oxides are vaporized by an electron beam, and the rotating glass target is evenly coated with many thin layers. The resulting color is determined by the individual oxide compositions.

Dichroic coatings transmit certain wavelengths of light, while reflecting others, thus creating an interference-effect similar to the iridescence observed in Nature's fire opal, dragonfly wings and hummingbird feathers. The transmitted color is different than the reflected color, and a third color is produced by viewing the dichroic piece at a 45o angle. The resulting colors are pure, saturated, single wavelengths of light, that appear to originate from within the dichroic piece.