Zerodur is available in three expansion classes. Zerodur is readily available and easily workable. Astrosital properties Astrosital is a Russian equivalent of Zerodur and is available in large sizes. The physical and thermal properties are slightly different from those of zerodur. Astrosital is readily available and easily workable.
Small blanks are available for very reasonable prices.
This glass is used primarily for large professional telescopes. ClearCeram-Z is a recently developed low expansion glass ceramic material from Ohara Corporation. This is a relatively recent innovation in mirror substrate materials mnufactred from sheets of fusion bonded and heat-treated plate glass and is manufactureed by ASM Products. The expansion coefficient slightly lower than pyrex, but much higher than the other glass ceramics. Mirror blanks are inexpensive and readily available.