Method of making crystallized glass

A method of making a crystallized glass article substantially free of microcracking, comprising:

• a. preparing a glass batch consisting essentially of
• i. a silica,
• ii. an alumina,
• iii. a lithium family glass batch ingredient consisting of a lithium salt, and
• iv. a zinc salt in an amount sufficient to provide a crystallized glass article from said glass batch having a ZnO content, percent by weight on an oxide basis of 1 to 4.0, which crystallized glass article obtained is characterized by the presence of microcracks in the surface thereof
• b. adding to said glass batch an alkali metal salt wherein the alkali metal is a member of the group consisting of potassium, rubidium and cesium, said alkali metal salt being present in an amount sufficient to provide a glass article upon cooling a melt of said glass batch having a content of an oxide of the alkali metal of said salt, percent by weight on an oxide basis of 0.15 to 2.50,
• c. melting the glass batch containing the ingredients set forth in (a) and (b) to form a glass melt,
• d. cooling said glass melt and subsequently therewith,
• e. forming a glass article,
• f. heat treating said glass article at a temperature and for a time sufficient to form crystals throughout the glass article and to form a crystallized glass article having surfaces thereof substantially free of microcracks.