So what is dichroic glass?
Well dichroic means two colours so you get a shifting of colour from this glass. It has a reflection colour (where the light bounces off the surface) and a transition colour (where the light goes through the glass)
Dichroic black backed glass
Dichroic glass is made up of hundreds of layers of quartz crystals and metal oxides, these are sprayed on to a spinning circle of glass in a vacuum chamber. This means you get even coverage on the glass.
Dichroic clear glass
The origin of dichroic glass is as hard to pin down as an urban legend all that is conferable is that it was discovered in California in the 60's. It has many uses for example: lighting, sculpture, film making and it is used by NASA for various things.
Basically for glass artists it means an amazing array of colour to play with.