Evaluation of a large glass-ceramic mirror blank.

A statistically designed study was performed to evaluate the homogeneity of selected properties of a large CER-VIT C-101 glass-ceramic mirror blank. A blank 1.9 m in diameter and 0.3 m thick weighing approximately 2180 kg was sampled to determine if the chemical composition, the density, the birefringence, and the linear coefficient of thermal expansion were dependent on the position within the blank. The blank had good homogeneity. The properties varied little throughout the blank, except for birefringence, which varied systematically with position.