Lead- and barium-free crystal glass
A lead- and barium-free crystal glass having a refractive index of at least 1.55, with in % by weight, more than 50% and less than 60% SiO 2 , more than 0.6% and less than 4% B 2 O 3 , less than 3% K 2 O, more than 12% and less than 15% Na 2 O, more than 4% and less than 11% CaO, more than 0.25% and less than 5% Al 2 O 3 , less than 2% MgO, and between 8 and 16% ZnO, with the proviso that the total content of the oxides of Pb, Ba and As is below 0.1%, the total content of the oxides of Ti and La is below 5% and the total content of the oxides of Nb, Ta, Yb, Y, W, Bi and Zr is below 5%, wherein at most 1% oxides of Nb, Ta and Yb respectively and 3% of the oxides of Y, W, Bi and Zr respectively are included.
1. A lead- and barium-free crystal glass having a refractive index of at least 1.55, with in % by weight
more than 50% and less than 60% SiO 2 ,
more than 0.6% and less than 4% B 2 O 3 ,
less than 3% K 2 O,
more than 12% and less than 15% Na 2 O,
more than 4% and less than 11% CaO,
more than 0.25% and less than 5% Al 2 O 3 ,
less than 2% MgO,
between 8 and 16% ZnO,
with the proviso that
the total content of the oxides of Pb, Ba and As is below 0.1%,
the total content of the oxides of Ti and La is below 5% and
the total content of the oxides of Nb, Ta, Yb, Y, W, Bi and Zr is below 5%,
wherein at most 1% oxides of Nb, Ta and Yb respectively and 3% of the oxides of Y, W, Bi and Zr respectively are included.
2. A crystal glass according to claim 1 wherein the total content of ZnO and CaO is over 15%.
3. A crystal glass according to claim 1 wherein CaO is partially replaced by SrO.
4. A crystal glass according to claim 1 additionally containing 0.5–3.0% Li 2 O.
5. A crystal glass according to claim 4 wherein the sum of Na 2 O and Li 2 O is below 17%.
6. A crystal glass according to claim 1 wherein the total content of all other constituents apart from purifying agents such as Sb 2 O 3 and decoloration agents such as Nd 2 O 5 and Er 2 O 3 is below 2%.