• Most frequently used material when glass is called for in ophthalmic eyewear.
• Consists of about 70% sand, 11%-13% calcium oxide or lime and 14% - 16% soda.
• Relatively strong provided surface is free from defects such as scratches or pits.
• Cleans easily and resists corrosion.
• Can be rendered impact resistant through either heat or chemical methods.

Flint Glass:

• Also known as lead glass. High index of refraction makes it suitable for use in the manufacturing of fused glass multifocals.
• Consists of 45% - 65% lead oxide, 25% - 45% sand, and 7% -10% soda.
• High specific gravity and low V-value result in heavy weight and increased dispersion.
• At one time it was used for single vision lenses of reduced thickness which was commercially known as �Thinlite.� However these are no longer available due to difficulties in rendering them impact resistant.

Barium Glass:

• High index of refraction combined with relatively low amount of chromatic dispersion, make this the material of choice for the fused segment of most glass multifocals manufactured today.
• Consists of 25% - 40% barium oxide in addition to sand and other metallic oxides.