Patent ID: 8883663

Claim:
A translucent or opaque glass-ceramic whose composition lies within the SiO 2 —R 2 O 3 —Li 2 O/Na 2 O—TiO 2 system and comprises a silicate crystalline phase, and a composition, in weight percent on an oxide basis, of 40-80% SiO 2 , 2-30% Al 2 O 3 , 2-10% Li 2 O, 0-8% TiO 2 , 0-3% ZrO 2 , 0-2% SnO 2 , 0-7% B 2 O 3 , 0-4% MgO, 0-12% ZnO, 0-8% BaO, 0-3% CaO, 0-6% SrO, 0-4% K 2 O, from greater than 0% up to 3% Na 2 O, 0-1.0% Sb 2 O 3 , 0-0.25% Ag, 0-0.25% CeO2, 0-0.01% Au, a molar ratio of Li 2 O+Na 2 O/Al 2 O 3 +B 2 O 3 of greater than 0.8, wherein the glass-ceramic is made from a glass that exhibits a liquidus viscosity of greater than 75,000 poise, and a molar ratio of Na 2 O to Li 2 O increases from a surface to a bulk of the glass-ceramic, wherein R 2 comprises at least one of B and Al.