(Frequently Asked Questions.)

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Lost Foam

Lost foam casting is COOL!
Until you do it, you don't quite beleive it will work, but it does.
In it's simplest form, the foam is shaped as desired (including a sprue), placed in firmly packed dry, loose sand, and poured with molten metal. The hot metal vaporizes the foam and hardens before the sand has a chance to move. The resulting casting (if done correctly) is a faithful reproduction of the foam pattern right down to any bead structure and fingerprints left in the glue.
Of course there are variations and details not yet explained, but you get the idea.
Some advantages of Lost Foam Casting are
You can quickly throw together a simple pattern or just use a piece of scrap foam to pour an ingot or to make a billet to be machined.
Some disadvantages are
When you pour the metal in a lost foam mold, there will be a great plume of hot smoke and noxious gases that will probably light on fire. Do NOT bend over the mold as you pour! Make every effort not to breath these fumes. A small fan blowing from your back across the mold will help a lot.

Here is a short video
from Dave Drecher showing the smoke and flame :

Subjects yet to be covered:

Shaping the foam
Optional investment
Embedding the foam in the sand
Pouring the mold