FIELD OF THE INVENTION
[0001] The present invention relates to the field of glass production. More
particularly, the present invention pertains to unique glass compositions and methods
5 for converting such compositions to opal and opalescent glass articles possessing
high chemical durability.
We claim:
1. A fluoride-free spontaneous opal glass demonstrating a dense, milky-white
appearance, excellent resistance to weathering and acid present in food and attack by
alkaline detergents consisting essentially, a softening point greater than 740° C and
5 less than 760° C, and containing the following composition essentially in terms of
weight percent on the oxide basis as calculated from the batch of, 59.2-71.3% SiO2,
11.2-19.32 % M2 O, 2.8-5.58% BaO, 3.1-5.86% Al2 O3, 2.9-8.9% B2 O3, 2.8- 5.1%
CaO, 0.3-2.2 % ZnO and 2.9-6.8% P2 O5, wherein
the ratio by weight of M2O to P2O5 being in the range 1.8 to 6.4 ;
10 the ratio M2O to CaO being in the range 2.3 to 6.8;
the sum of Barium Oxide (BaO) and Zinc Oxide (ZnO) should be at least 3.6% by
weight;
the total of the weight quantities of the ingredients amounting to 100%, having said
that the opal glass has a thermal expansion coefficient of 8.5-9.1 x 10-7 /°C, in the
temperature range of 50-300°C, a density of at least 2.4 g/cm3 15 and level of opacity
greater than 80%.
2. A fluoride-free spontaneous opal glass set forth in claim 1, characterized in that it
has the following composition 59.9-68% SiO2, 12.8-17.3 % M2 O, 3.2-5.1% BaO,
3.5-5.3% Al2 O3, 3.1-7.9% B2 O3, 2.97- 4.8% CaO, 0.4-1.8 % ZnO , and 3.2-6.3% P2
20 O5.
3. A fluoride-free spontaneous opal glass set forth in claim 2, characterized in that the
ratio by weight of M2O to P2O5 being in the range 2.35 to 3.75 ;
4. A fluoride-free spontaneous opal glass set forth in claim 2, characterized in that the
ratio M2O to CaO being in the range 3.3 to 4.7;
25 5. A fluoride-free spontaneous opal glass as claimed in claim 1, wherein M2O is at
least