Hard Light Conductive Glass

Also known as circuit glass.
Special glass made from sand blended with ignium. Hard light fed into it is contained and molded to the shape of the object (directed by grooves etched into it). Note that this isn't internal reflection. That being said, the material does exhibit something similar to internal reflection with magical energy- energy within the medium tends to stay contained, while energy outside is reflected. This gives it insulative properties from outside sources of magical energy, despite being an excellent conductor. Internally etching the material (similarly to laser-etching glass, only using extremely finely manipulated light magic) can be used to create paths for the projections to focus along.
Used to form hard light circuitry components, such as relays (using arcmagnetic steel) and optical fibers. Notably, optical fiber ropes containing active hard light are beholden to typical hard light rules, and remain perfectly rigid (although extremely fragile due to the low amounts of power seen in circuitry) while powered.
This specialized glass is also used to form mirrors for magical energy in order to focus it. This is often used on the inside of enchanters' kilns etc. to reduce leakage.
A tougher material with similar magical properties exists, known as Aloxidilith Glass .