Abstract: The present invention relates to glass-ceramic materials, processes for making the same and articles comprising the same. The glass-ceramic material has a composition, by weight of the total composition, comprising 55-68% SiO2; 18-24% Al2O3; 3.3-4.1% Li2O; 1.5-4.0% ZnO; 1.5-5.0% MgO; 2-5% TiO2; 0-2% ZrO2; 0-5% B2O3; 0-8% P2O5; 0-2% Na2O, 0-2% K2O; and at least one component resulting from an effective amount of at least one fining agent; wherein: the total of B2O3 and P2O5 is at least 1.5% by weight, the total of MgO and ZnO is at least about 3.5% by weight, the total of Na2O and K2O is less than about 3.0% by weight, the total of P2O5, B2O3, Na2O and K2O is less than about 11% by weight, the weight ratio of the sum total of Na2O+K2O to the sum total of P2O5+B2O3 ( Na 2 ? O + K 2 ? O B 2 ? O 3 + P 2 ? O 5 ) is less than about 0.

Abstract: The invention concerns glasses that have a refractive index of more than 1.880, an Abbe number of more than or equal to 30.4, and a density of more than 4.1, and having the following chemical composition, expressed in wt. %, based on the oxides: SiO.sub.2 : 6-9, B.sub.2 O.sub.3 : 15-19, with SiO.sub.2 +B.sub.2 O.sub.3 <26, Nb.sub.2 O.sub.5 : 12 to <20.5, ZrO.sub.2 : 8-10, TiO.sub.2 : 7-11, La.sub.2 O.sub.3 : 23-32, with ZrO.sub.2 +TiO.sub.2 +La.sub.2 O.sub.3 : .gtoreq.44, CaO: 8 to <13, SrO: 0-2, BaO: 0-2, MgO: 0-2, ZnO: 0-5, with CaO+SrO+BaO+MgO+ZnO: .gtoreq.9, Y.sub.2 O.sub.3 : 0-5, WO.sub.3 : 0-5, Li.sub.2 O+Na.sub.2 O+K.sub.2 O: 0-2, others 0-1.