A mixture of special sand (silica) with traces of other elements such as boron, phosphorus, and lead. These ingredients are melted together at a temperature of about 1650° C. (3000° F.). The newly formed glass, when cooled, is noncrystalline, smooth, extremely hard, and quite brittle. Volcanic heat has produced a form of glass called obsidian, and lightning, when striking sand, sometimes fuses it into long, slender tubes of glass known as fulgurites.

In Egypt have been found glass beads that archaeologists believe were made some 4,000 years ago, about the time Abraham was born. Job, who lived in the 17th century before the Common Era, names glass alongside gold for preciousness when he says: “Gold and glass cannot be compared to [wisdom].”​—Job 28:17.

The apostle John, in describing his visions, makes mention of “clear glass” and “transparent glass” (Re 21:18, 21); also of “a glassy sea like crystal.”​—Re 4:6.