Patent ID: 7897531

Claim:
Glass comprising, in mass %, SiO 2 20.0-35.0% TiO 2 1.0-less than 21.0% La 2 O 3 5.0-less than 25% CaO 0.0-less than 15.0 % MgO + CaO 0.0-less than 16.0% ΣR 2 O (R is at least one selected from Li, Na, K and Cs) 0.1—less than 15.0% Li 2 O in a range from 0 to 4.75 mass %, and Nb 2 O 5 in a range from 0 to 13.64 mass %, wherein a ratio of contents in mass % of B 2 O 3 /SiO 2 is within a range from 0 to 0.5, wherein said glass has optical constants of a refractive index (nd) of 1.79 or over, an Abbe number (vd) of 27 to 35 and a specific gravity (D) of 3.20 or over, and chemical durability of Class 1 according to the Powder Method (acid-proof property RA according to the Powder Method), wherein relation between the refractive index (nd) Y and specific gravity (D) X is Y≧0.175X+1.137, and wherein said glass is free from devitrification in the interior of the glass in a reheat test.