# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DY-qo7Ryoj9
- **Gondola URL:** https://gondola.cc/posts/66053058-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/13af11b2d6.jpg
- **Posted:** 2026-05-30T22:14:10.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

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 carbonate and dropping silica gel out of solution. Seconds, not hours.
	•	Ester curing. A slow organic ester hydrolyses, gently lowering pH and gelling the bond uniformly through the section.
	•	Dehydration. Drive off the water and the silicate concentrates until it gels on its own.

The trade-off is the sodium itself. Residual Na2O acts as a flux, lowering the softening point of the bond and capping how hot you can pour before the shell sags or reacts. It also resists shake-out, since a fully cured silicate bond does not want to crumble.

Cheap, water based, no solvent fumes, fast to set. For the right alloy at the right temperature, sodium silicate remains a quietly elegant piece of chemistry.

#stemantics #materialscience #metalcasting #foundry #chemistry

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## Tags

metalcasting, foundry, materialscience, chemistry, stemantics

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