Dichroic glass can display fantastic and vibrant colours, as in this necklace produced by Beryl:

The colours present in dichroic glass are produced by a number of very thin layers of metal oxides which are so thin they need the glass to produce mechanical stability. The layers of oxides create an "interference filter" which can produce very precise colour transmission and reflection.

Glass is used to provide strength as it is transparent, stable, withstands large temperature variations and not affected by moisture, solvents or acids.

If the dichroic glass is backed with clear glass, it will produce totally different colours depening upon whether the light is reflected off its surface, or the light source is behind the object: 

Below is the same piece of glass photographed with reflected, then trasnmitted light:

The coatings are produced by vacuum depositing multiple thin layers of oxide onto a glass substrate. A vacuum chamber is needed in order to produce a pure environment for depositing the thin film materials. The vacuum produced is similar to that of outer space. The oxides are vaporized in a crucible located in the bottom of the vacuum chamber, by a high voltage electron beam onto the rotating glass above. The glass is also rotated in the chamber through this vaporization process in order to deposit uniform coatings on the glass.  

The complete process may require from 15 to 50 distinct layers (steps) of alternating metallic and silicon oxides. The total thickness of the oxide layers may total no more than 70 nanometers . To put things in perspective, a human hair is 70,000 nanometers; the wavelength of violet light is 400 nanometers and red light is 700 nanometers. The dichroic coating creates an optical filter that transmits (passes) certain wavelengths of light and reflects (blocks) others.  

Click on the picture to see a small gallery of Dichroic jewellery Bee has made.