Water glass is one of the oldest tricks in the foundry, and it still earns its place. Add sodium silicate to a casting dip and you are pouring in a liquid that can become glue, ceramic, and structural skeleton all at once. Sodium silicate is a solution of silica and soda, written Na2O.nSiO2. That little “n” is the whole story. It is the modulus, the silica to soda ratio, usually sitting between about 2 and 3.3. Push it silica rich and the bond is stronger and more refractory. Push it soda rich and it stays water soluble and easier to break down later. In a dip or slurry it does one job: it binds loose refractory grains into a coherent shell. The mechanism is gelation. Dissolved silicate is a tangle of polymerised SiO4 units held apart by sodium ions and water. Strip away that stabiliser and the network collapses into a solid silica gel that locks every grain in place. Three common ways to trigger the set: • CO2 gassing. Carbon dioxide reacts with the silicate, forming sodium carbo...