Patent ID: 8047021

Claim:
A process for the preparation of a lithium silicate blank, which comprises: (a) producing a melt of a starting glass containing the initial components SiO 2 , Li 2 O, K 2 O, Al 2 O 3 and P 2 O 5 or other nucleation agent as the main components, (b) pouring the melt of the starting glass into a mould to form a starting glass blank and cooling the glass blank to room temperature, (c) subjecting the starting glass blank to a first heat treatment at a first temperature to give a glass product which contains nuclei suitable for forming lithium metasilicate crystals, or (b′) pouring the melt of the starting glass into a mould to form a starting glass blank and cooling the glass blank to a first temperature, (c′) holding the starting glass blank at the first temperature to give a glass product which contains nuclei suitable for forming lithium metasilicate crystals, (d) subjecting the glass product of step (c) or (c′) to a second heat treatment at a second temperature which is higher than the first temperature to obtain the lithium silicate blank with lithium metasilicate crystals as the main crystalline phase, (e) cooling the lithium silicate blank having the lithium metasilicate crystals as the main crystalline phase.