High Refractive Index Glasses With Low Dispersion

Optical glasses are made from batches containing a low proportion of silica, but a high percentage, preferably more than 50, of one or more of the oxides of metals in the even series of Groups III, IV, and V of the periodic system having an atomic weight greater than 47. The preferred oxides are those of titanium, zirconium, lanthanum, tantalum, and thorium. Tungesten oxide also is suitable and the oxides yttrium, columbium, and hafnium may be used. Boric oxide may be used as a flux, and small amounts of alkali metals may be included. Preferably silica is not included or not more than 10% is used.