1. 
   Zerodur
   Zerodur®, a registered trademark of Schott Glass Technologies, is a lithium aluminosilicate glass-ceramic produced by Schott AG since 1968. It has been used for a number of very large telescope mirrors including Keck I and Keck II. With its very low coefficient of thermal expansion it can be used ...
   Found op http://en.wikipedia.org/wiki/Zerodur
   
   
2. 
   Zerodur
   (from the article `telescope`) ...better materials for mirrors have become available. Cer-Vit, for example, was used for the 4.2-metre William Herschel Telescope of the Roque de ...
   Found op http://www.britannica.com/eb/a-z/z/6
   
   

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