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Primary ingredients for Roman glassmaking

Naturally colored glass is composed of 72% silica, 15% soda, 10% lime, and 3% other impurities. Beach sand, the main ingredient in glass, contains silica and lime, the latter component coming from crushed shells. There are two steps to producing naturally colored glass:

(1) melting the ingredients at a relatively low temperature (circa 750 degrees C) to obtain a white, granular substance (frit) that could easily be stored for later use;

(2) re-melting the frit in a far hotter furnace (circa 1150 degrees C), thereby transforming it into fluid glass.