A range of CaO-Al203-Si02 glasses have been prepared by fusion of pure starting materials in platinum crucibles. Compositions containing large amounts on network formers, Al203 and Si02, are difficult to crystallize. If the amount of network former is reduced, glasses will self-nucleate and crystallize more readily, but the products of crystallization tend to react with water. This conflict has been partly resolved by adding Mg0 and Zn0 and tailoring compositions so as to produce a phase, variously designated "Q" or "pleochroite". Pleochroite crystallizes with a typically fibrous morphology. Preliminary experiments on fragments and melt-cast glass rods indicate that these compositions can be heat treated without deformation to yield highly crystalline, transparent ceramics.
