Method of manufacturing crystalline glass articles

Claim 1

A method of making a crystalline glass product comprising the steps of melting a batch mix until a glass is obtained in which the main components are taken in the following quantities, in weight per cent: SiO2, 45 to 69; CaO, 18 to 45; and Al2O3, 2 to 22; and sulfur sulfide in an amount from 0.3 to 0.5 per cent, at least a stoichiometric quantity of iron ions, and further additives of Na2O, up to 5 per cent, and fluorine, up to 2 per cent; shaping a blank while the glass mass being shaped is cooled down to a temperature of 670*-750*C at which crystallization centers in the form of FeS are formed; holding the product at said temperature; raising the temperature to 930*-970*C at a rate of 75-320'''' an hour; holding the blank at said temperature in order to attain from 60 to 80 per cent of the maximum possible crystalline phase; gradually cooling the blank to room temperature; cutting out a product from said blank; heating said product to a temperature of 930*-970*C; holding said product at said temperature for 1.5 to 3 minutes per each millimeter of thickness of said product, and cooling the product at a rate of 85*-250* per minute.