Patent ID: 8048816

Claim:
A composition suitable for ceramming to make a colored, machinable glass-ceramic article, said composition, as batched, comprising in weight percent: (i) a colorant in an amount of 0 wt %<colorant≦3 wt %, except that when the colorant is iron the colorant is present in an amount of 0 wt %<colorant≦20 wt % and (ii) a precursor glass composition selected from the group of: a. compositions containing a trisilicic mica phase after ceramming that consists essentially of 25-60% SiO 2 , 5-25% Al 2 O 3 , 5-15% B 2 O 3 , 5-25% MgO, 4-20% F, 0-7% Li 2 O, 0-15% K 2 O, 0-15% Na 2 O, 0-15% Rb 2 O, 0-20% Cs 2 O, 2-20% total of K 2 O+Na 2 O+Rb 2 O+Cs 2 O, 15-35% total of Al 2 O 3 +B 2 O 3 and 6-25% total of MgO+Li 2 O; and b. compositions containing a non-alkali-oxide-containing mica phase after ceramming that consists essentially of 30-65% SiO 2 , 5-26% Al 2 O 3 , 10-35% MgO, 4-12% F, 5-25% SrO and 0-25% BaO.