Artist: Roman Empire/Palestine
Title: Double Cosmetic Tube, 200-400 A.D.

Gift of Walter P. Chrysler, Jr.

CALCIUMCalcium Carbonate
Batch: Stabilizer

Although fluxes play an important role in making the glassmaking process practical, they also leave glass water-soluble. A compound must be added to the batch in order to create an arrangement of molecules that will not react with water. These are known as stabilizers, and they make up approximately 10% of ordinary batch.

In the early stages of glass use, Roman artisans added small amounts of calcium carbonate (CaCO3), or limestone, to stabilize the batch. Even with calcium carbonate, glass buried in the ground interacted with the moisture in the soil. When excavated many years later, the surface of the objects had become iridescent.