Casting sand stuff?

[Major Fallout]

Years and years ago I was at an autojumble and someone was demonstrating aluminium casting. For a small fee I put my hand in the sand and they pushed some sort of gas into it and the sand went hard. They then used this as the mould.

Has anyone got any idea what it was?
I want to have a go at some stuff myself.

[Atomic GTI]

https://www.google.com/search?q=co2+setting+sand+f...

[Major Fallout]

Thats the stuf! Thank you!

I was searching for "gas setting casting sand" and wasnt getting anywhere.