Dichroic Glass
From Melting Pot Wiki
Dichroic glass is a glass containing multiple micro-layers of metal oxides, with a total thickness of three to five millionths of an inch, which gives the glass dichroic optical properties.
Uses: A plate of dichroic glass can be fused with other glass in multiple firings. Certain wavelengths of light will either pass through or be reflected, causing an array of color to be visible. Due to variations in the firing process, individual results can never be exactly reproduced; each piece of fused dichroic glass is unique.