A black β-spodumene glass ceramic is provided. The glass ceramic includes β-spodumene as a primary crystal phase and gahnite as a minor crystal phase. The glass ceramic is characterized by the color coordinates: L*: 20.0 to 40.0, a*: −1.0 to 0.5, and b*: −5.0 to 1.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

A black β-spodumene glass ceramic is provided. The glass ceramic includes β-spodumene as a primary crystal phase and gahnite as a minor crystal phase. The glass ceramic is characterized by the color coordinates: L*: 20.0 to 40.0, a*: −1.0 to 0.5, and b*: −5.0 to 1.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

Disclosed is a pre-sintered ceramic block for a dental restoration, which has a low pre-sintering temperature, contains a silica main crystal phase, but does not contain or contains a small amount of lithium metasilicate crystal phase. The pre-sintered ceramic block has a low hardness, with a Vickers hardness of 0.5-3 GPa, which is significantly lower than that of a ceramic block containing a lithium metasilicate crystal phase, and same is suitable for dry machining and also wet machining when being machined into a dental restoration. (FIG. 2)

Disclosed is a pre-sintered ceramic block for a dental restoration, which has a low pre-sintering temperature, contains a silica main crystal phase, but does not contain or contains a small amount of lithium metasilicate crystal phase. The pre-sintered ceramic block has a low hardness, with a Vickers hardness of 0.5-3 GPa, which is significantly lower than that of a ceramic block containing a lithium metasilicate crystal phase, and same is suitable for dry machining and also wet machining when being machined into a dental restoration. (FIG. 2)

The present application provides transparent glass-ceramics of β-quartz of composition containing a small content of lithium, articles constituted at least in part of said glass-ceramics, glasses precursors of said glass-ceramics, and also a method of preparing said articles. Said glass-ceramics have a composition, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed as percentages by weight of oxides, containing: 62% to 68% of SiO.sub.2; 17% to 21% of AI.sub.2O.sub.3; 1% to <2% of Li.sub.2O; 1% to 4% of MgO; 1% to 6% of ZnO; 0 to 4% of BaO; 0 to 4% of SrO; 0 to 1% of CaO; 1% to 5% of TiO.sub.2; 0 to 2% of ZrO.sub.2; 0 to 1% of Na.sub.2O; 0 to 1% of K.sub.2O; with Na.sub.2O+K.sub.2O+BaO+SrO+CaO<6%; optionally up to 2% of at least one fining agent comprising SnO.sub.2; and optionally up to 2% of at least one coloring agent.

The present application provides transparent glass-ceramics of β-quartz of composition containing a small content of lithium, articles constituted at least in part of said glass-ceramics, glasses precursors of said glass-ceramics, and also a method of preparing said articles. Said glass-ceramics have a composition, free of arsenic oxide and antimony oxide, except for inevitable traces, expressed as percentages by weight of oxides, containing: 62% to 68% of SiO.sub.2; 17% to 21% of AI.sub.2O.sub.3; 1% to <2% of Li.sub.2O; 1% to 4% of MgO; 1% to 6% of ZnO; 0 to 4% of BaO; 0 to 4% of SrO; 0 to 1% of CaO; 1% to 5% of TiO.sub.2; 0 to 2% of ZrO.sub.2; 0 to 1% of Na.sub.2O; 0 to 1% of K.sub.2O; with Na.sub.2O+K.sub.2O+BaO+SrO+CaO<6%; optionally up to 2% of at least one fining agent comprising SnO.sub.2; and optionally up to 2% of at least one coloring agent.

A black β-spodumene lithium disilicate glass ceramic is provided. The glass ceramic includes at least one of magnetite, β-quartz, cristobalite, and lithium phosphate as a minor crystal phase. The glass ceramic is characterized by the color coordinates: L*: 15.0 to 35.0, a*: −3.0 to 3.0, and b*: −5.0 to 5.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

A black β-spodumene lithium disilicate glass ceramic is provided. The glass ceramic includes at least one of magnetite, β-quartz, cristobalite, and lithium phosphate as a minor crystal phase. The glass ceramic is characterized by the color coordinates: L*: 15.0 to 35.0, a*: −3.0 to 3.0, and b*: −5.0 to 5.0. The glass ceramic may be ion exchanged. Methods for producing the glass ceramic are also provided.

A decorative glass article is substantially free of lead oxide, and has a refractive index of 1.9 or more and an Abbe number of 42 or less.

A decorative glass article is substantially free of lead oxide, and has a refractive index of 1.9 or more and an Abbe number of 42 or less.