Dichroic, Greek for "two lights", is a dynamic art-glass medium that transmits and reflects color. The medium is created through vacuum deposition. The gloss is attached inside a controlled temperature vacuum and spun.

Chemicals are introduced, forcing on ultra -thin quartz crystal structure to grow on the surface of the glass. The crystal structure "literally bends light, creating a wonderful art-glass medium.

What is it.

Dichroic glass is a high-tech spin-off of the space industry. “Dichroic” is defined as the property of having more than one color, especially when viewed from different angles or from transmitted to reflected light. Dichroic coated glass is produced by a process called “thin film physics” and is generally referred to as a color separator. It’s normally used as an interference filter in scientific measuring or correcting applications. To get this effect, 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 gyro-pump, and the chamber is heated to 300 degrees Fahrenheit. The metallic oxides are vaporized by on electron beam, and the rotating glass target is evenly coated with many thin layers. The resulting color is determined by the individual oxide compositions and the coatings sequence, totaling about 700 angstroms thick, (3-5 millionths of an inch). All of this is tightly controlled by a computer. Since the total thickness is so minute, the filter 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. It is transparent, has adequate rigidity, is stable, withstands relatively high temperatures, and is not affected by moisture, solvents or most acids.

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 when the light rays transmit straight through the glass they are less effected by refraction than when passing at an off axis angle, which make the light travel a greater distance through the glass. It is this distance that causes a color shift. When dichroic glass is viewed at even slightly different angles, you will see a variety of different colors as you rotate it. When you rotate the filter from viewing directly through it the intermediate colors will shift down the rainbow. Each dichroic glass color must be individually engineered. There is no magic material that makes precisely the color you want, or some mythical high-tech machine that allows you to press the blue button and get blue dichroic glass off the conveyer belt. Each film structure is different depending on which spectra of light we want to reflect away. As an example: magenta transmission requires us to reflect away all the green light, allowing the blue violet, orange and red light to transmit through. That particular structure requires 19 layers work of reflections to remove the light we wish from transmitted spectra. Not all colors are so easy to achieve, green transmission is just the opposite of the magenta. To get a green transmission, we have to reflect away all the light except the green. That structure requires 49 layers. This sounds like a big, thick coating, but if you add all those layer thickness together, the total coating thickness will still be less than one thousandth of a millimeter.

The dichroic colors are usually coated on either clear or black glass. The glass being coated can be a flat or rippled glass and the color will differ on the different textures.

From an article by Carolyn Beebe - The Dichroic Lady

What is Dichroic?

Definitions of Dichroic on the Web:
Glass that has been coated with a thin layer of metallic oxide. Dichroic coatings transmit certain wavelengths of light while reflecting others, creating an interference effect similar to iridescence.
www.northstarglass.com/glossary.asp

A type of manufacturing glass, which has ability in two different ways. Color is transmitted through the glass and complimentary colors are reflected from the surface.
www.glasscons.com/gloss.html

A lay term used to describe glasses that have been coated with more than one ultra-thin crystalline layers of transparent metal oxide. Dichroic glass was designed to enhance reflections at specific wavelengths of light.
www.atouchofstainglass.com/sectionA.html