A glass-ceramic for a magnetic disk substrate in which the grain size can be controlled and the surface roughness after polishing is within the range from 15 .ANG. to 50 .ANG. is provided by heat treating a base glass including in weight percent:...http://www.google.de/patents/US5391522?utm_source=gb-gplus-sharePatent US5391522 - Glass-ceramic for magnetic disks and method for manufacturing the same
