In article ,
mark wrote:

Could a person melt brass or bronze with a oxy welding torch in a
cruxible and pour it in a shallow, crude mold of plaster paris or some
other material? I've been reading about sand cast molds but it looks
like too much of a skill to learn for a small project. Thank you.

Plaster is a bad idea for casting metal unless you've kilned it
*TOTALLY* dry - Otherwise, the explosions tend to turn the project into
a whole bunch of broken plaster and spilled molten metal running down
the stand/your leg/across the floor/etc. Problem is, once you bake it
hot enough to be safe to pour metal into, plaster goes all brittle and
crumbly, and doesn't hold together worth diddly.

Plaster works the same way as cement or concrete or mortar - It doesn't
actually "dry", it "sets". Most of the water you mix it with is trapped
in the finished item, held captive in the crystal structure, with only a
small part of it evaporating. Depending on the thickness of the piece,
the "set" process can literally go on for years - They say that the
interior of the Hoover Dam is *STILL* setting, and will likely continue
to do so for another hundred years or longer before the process
completes and the concrete reaches its full strength. Ditto plaster
pieces - A large enough piece will take years to *FULLY* set, even
though it's usually solid enough to unmold and handle in 20 minutes. But
I digress...

When you dump 700+ degree metal onto unbaked plaster, the trapped water
explodes into steam almost instantly, usually tearing the mold apart,
and possibly flinging molten metal at you in the process. (Concrete
floors usually spall instantly if molten metal is spilled on them, too -
Exactly the same process is in action for both materials)

Nobody has ever given me a satisfactory explanation for the "why" of it,
but in my experience, baking plaster to get all the water out of it
almost always results in a piece that has lost all strength, and is
likely to crumble at the slightest touch.

The "damned if you do, damned if you don't" of plaster (and its "kissin'
cousins", cement, mortar, and concrete) can be truly frustrating
sometimes.

--
Don Bruder - - If your "From:" address isn't on my whitelist,
or the subject of the message doesn't contain the exact text "PopperAndShadow"
somewhere, any message sent to this address will go in the garbage without my
ever knowing it arrived. Sorry... http://www.sonic.net/~dakidd for more info