GLASS is an inorganic product made of very carefully selected silica sand mixed with soda, ash, potash, lead or lime, and other components fused together at a very high temperature.
Glassware usually sold over the counter to retail customers is most generally divided into 3 classes, lime glass, lead glass and borosilicate glass or heat resisting glass.
Lime glass contains a substantial proportion of lime usually processed with soda or other alkalis to produce a quick-setting brilliant glass extensively used in tumblers, tableware and less expensive decorative ware.
Lead glass, always containing a substantial portion of lead oxide combined with potash or other alkalis, is generally used in producing high quality stemware, tableware, vases and other ornamental glassware. Brilliance, weight, dearness, and resonance can be distinguishing features. Lead glass is particularly adaptable for cutting because of its softer texture and relatively high index of light refraction.
Borosilicate glass usually has at least 5% of boric oxide designed to make the glass able to withstand greater thermal shock because of its relatively low coefficient of expansion. This characteristic enables this glass to be successfully used in the manufacture of oven (baking) ware and with process and formula changes makes it able to withstand direct contact with open flame. This latter ware is commonly called top-of-stove ware. Care should be exercised when using the words "heat resistant" not to imply that such articles may be used for top-of-stove cooking unless the manufacturer has assured that the article is made of glass that withstands open flame.