Patent ID: 7297647

Claim:
An optical lanthanum flint glass with chemical resistance and stability to crystallization, comprising in percent by weight [w/w]: SiO 2 0.1 to 5.5 B 2 O 3 27 to 35 La 2 O 3 42 to 48 BaO 0.1 to 5 ZnO 0.5 to 5 Y 2 O 3 6 to 12 TiO 2 0 to 4 ZrO 2 4 to 10 Nb 2 O 5 0 to 5 WO 3 0 to 5 wherein the ratio based on weight of La 2 O 3 :B 2 O 3 is ≦1.8, and wherein said glass has a refractive index of 1.73≦n d ≦1.82 and an Abbé value of 43≦v d ≦53, and is lead and arsenic-free.