Embedding material useful in preparing glass-ceramic products

Claim 1

An embedment material for use with glass castings which are subsequently heat treated to convert the glass into a glass-ceramic, said glass casting consisting essentially, expressed in terms of weight percent on the oxide basis, of ______________________________________ K.sub.2 O 10-18 Al.sub.2 O.sub.3 0-2 MgO 14-19 ZrO.sub.2 0-7 SiO.sub.2 55-65 F 4-9 ______________________________________ and said glass-ceramic exhibiting a coefficient of thermal expansion of about 70-90×10 -7 /°C., said embedment material, expressed in terms of weight percent, consisting essentially of 5-30% plaster of Paris and 70-95% leucite, or consisting essentially of 45-60% Al 2 O 3 , 25-35% cristobalite, 5-20% plaster of Paris, and 0-15% leucite, which material displays resistance to thermal deformation at a temperature between about 1050°-1150° C., demonstrates a coefficient of thermal expansion equal to or not more than 40×10 -7 /°C. units greater than that exhibited by said glass-ceramic, is subject to an inversion at a temperature below about 775°-825° C. accompanied with a change in volume of greater magnitude than that exhibited by said glass casting resulting from the thermal expansion thereof, and is inert to said glass and glass-ceramic, whereby the shrinkage customarily experienced during the densification of said casting as the glass is converted into a glass-ceramic is minimized and a sound glass-ceramic article of tight dimensional tolerances is produced.