Abstract: A glass composition for a substrate consisting essentially of from 56 to 72 wt % of SiO.sub.2, from 1 to less than 14 wt % of Al.sub.2 O.sub.3, from 0 to 9 wt % of MgO, from 0.5 to 11 wt % of CaO, from 0 to 4 wt % of SrO, from 0 to 3 wt % of BaO, from 6 to less than 14 wt % of MgO+CaO+SrO+BaO, from 0 to 9 wt % of Na.sub.2 O, from 6 to 20 wt % of K.sub.2 O, and from 6 to 20 wt % of Na.sub.2 O+K.sub.2 O.

Abstract: A glass composition for a substrate consisting essentially of from 59 to 72 wt % of SiO.sub.2, from 1 to 15 wt % of Al.sub.2 O.sub.3, from 0.5 to 9 wt % of MgO, from 0.5 to 11 wt % of CaO, from 0 to 6 wt % of SrO, from 0 to 5 wt % of BaO, from 4 to 19 wt % of MgO+CaO+SrO+BaO, from 0 to 9 wt % of Na.sub.2 O , from 4 to 21 wt % of K.sub.2 O, from 10 to 22 wt % of Na.sub.2 O+K.sub.2 O, and from 0.5 to 10.5 wt % of ZrO.sub.2, wherein the difference between the SiO.sub.2 content and the Al.sub.2 O.sub.3 content is from 50 to 71 wt %, and the specific gravity of the composition is less than 2.6.

Abstract: Abrasion resistant glass, which consists essentially of the following components:______________________________________ SiO.sub.2 75.5 to 85.5 (wt %), RO 1 to 8 (wt %), R'.sub.2 O 10 to 23.5 (wt %), RO + R'.sub.2 O 11 to 24.5 (wt %), Al.sub.2 O.sub.3 0 to 5 (wt %), ______________________________________ RO/R'.sub.2 O (weight ratio) at most 0.5,provided that R is at least one member selected from Mg and Ca, and R' is at least one member selected from Li, Na and K, and of which the density measured at room temperature is at most 2.41 g/cc.

Abstract: Abrasion resistant glass, which consists essentially of the following components:______________________________________ SiO.sub.2 74 to 85.5 (wt %), B.sub.2 O.sub.3 0.5 to 5 (wt %), SiO.sub.2 + B.sub.2 O.sub.3 76 to 88 (wt %), RO 1 to 9 (wt %), R'.sub.2 O 10 to 23 (wt %), RO + R'.sub.2 O 11 to 24 (wt %), Al.sub.2 O.sub.3 0 to 5 (wt %), RO/R'.sub.2 O (weight ratio) at most 0.6, ______________________________________provided that R is at least one member selected from Mg and Ca, and R' is at least one member selected from Li, Na and K, and of which the density measured at room temperature is at most 2.43 g/cc.

Abstract: Alkali metal- and alkaline earth metal-oxide aluminosilicate amorphous glass articles can be strengthened by providing such glass with a cerium dioxide sensitizer and a nucleating agent, irradiating the article with electromagnetic radiation, heating the irradiated article to a temperature between about the annealing and softening points of the glass, and cooling the heated, irradiated glass article. The treated article has a thick lower layer of the amorphous glass, but a thin layer of this glass at the surface of the article has been converted to a crystalline state. In this surface layer, some of the cerium has been converted from a +3 to a +4 ionic state and some of the metal element in the nucleating agent has been changed to a metallic state. The adjacent location of the lower and surface layers creates large compressive stresses at the surface layer which imparts great strength to the glass article.