1) Glass type 2) Transparent material
Found on
https://www.crosswordclues.com/clue/sitall
Sitall aka Sitall CO-115M or Astrositall, is a crystalline glass-ceramic with ultra low coefficient of thermal expansion (CTE). It was originally manufactured in the former Soviet Union and was used in the making of primary mirrors for the Russian Maksutov telescopes, but since dissolution has diminished in quality. Sitall has a CTE of only 0±1.5...
Found on
http://en.wikipedia.org/wiki/Sitall
No exact match found.
