| abstract |
This invention is directed to the formation of blue-to-black transparent glass-ceramic articles containing beta -quartz solid solution as essentially the sole crystal phase present therein. The articles are prepared by heat treating reduced precursor glass articles consisting essentially, in weight percent, of 2.5-5% Li2O, 1-2% MgO, 18-30% Al2O3, 2-4% TiO2, 1-4% ZrO2, 48-70% SiO2, 1-12% P2O5, and 0-2% ZnO. The precursor glass articles are placed in a reduced state through the inclusion of a sufficient amount of a hydrogen-containing phosphate and/or chloride and/or Ti2O3 to obtain about 0.2-6% of the total titanium content in the form of Ti+3 ions. |