just saw "how its made" and a street lighting company were making a sand core for an ali casting. The guy completely solidifies a "white sand" core by blowing co2 through it, to aparently start a "chemical reaction"

anyone ever seen or done this? seemed amazing to me

special sand??

[Edited on 6/9/09 by liam.mccaffrey]

Bit of googlage says it's probably sand and Sodium Silicate

This technique has been around for more than 60 years.
The sand is mixed with a resin which is activated by the prescence of CO2. This makes a solid core which can be handled and laid in the mould. When the mould is broken open the sand can easily crushed in a mill and re used.
The ability to build the core from a series of shaped blocks enables quite intricate castings to be made cheaply.