Ian wrote:
According to Wikipedia, glass is approximately 75% SiO2. Quartz is SiO2.

The use of fused quartz for UV and salt for IR is actually
something he is right about.

Ordinary glass only passes a small amount of UV close to the
visual spectrum. Lenses that go far into the ultraviolet
are made using fused quartz and fluorite elements. (This combination
gives excellent broadband colour correction so such lenses are
also used for near-infrared.)

Ordinary glass passes a fair bit of the IR spectrum but salt passes
much longer wave IR than glass does.

Peter.
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