Abstract: A composition which represents a new class of unleaded transparent vitreous ceramic which is described as an `Advanced or Combined Intermediate-Oxide Alkali Borosilicate. The composition comprises in combination a specially developed alkali borosilicate and a major addition selected from combinations of the group of traditionally accepted opacifiers, consisting of Zirconium, Tin, and Titanium, the said elements being present in said combination in amounts 0.5 to 43.9 wt % in terms of the Oxide form. The major addition will consist of at least two of said elements. The composition may include minor additions (.ltoreq.10 wt %) of any other element or elements which do not cause loss of transparency.

Abstract: The present invention relates to an unleaded durable transparent vitreous glass composition comprising a combination of(a) up to 98 wt % of a low alumina alkali borosilicate,(b) 2-20 wt % of a major addition of one element selected from the group of zirconium, tin and titanium, and(c) less than 10 wt % of at least one element selected from bismuth, barium, strontium, zinc, lanthanum, molybdenum, cerium and/or a fluoride containing inorganic compound wherein the amounts of (a), (b) and (c) are calculated on the basis of the total amount of the oxide forms of (a), (b) and (c),a process for its production and the use of said composition.