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You can save yourself a lot of trouble.  Lead casting in gypsum investments
is really pretty simple.  You can use alginate impression material for your
mold and gypsum stone for investment in a coffee can.  The secret to
removing water from the investment is to heat soak the investment in your
oven at 350 degrees for an hour or two before casting.  Use your propane BBQ
pit with the grill removed to melt the lead in a container suitable for
pouring.  Put the heat soaked coffee can in the BBQ pit and pour the
casting.  Remove the casting and wait long enough for the lead to harden.
Then throw the whole thing in a bucket of cold water and watch the plaster
explode away from your casting.

See my artical about two years ago in LNN for detailed description of this
process for the elevator counterweights.  You can contact me by e-mail with
specific questions.

Regards,
John Barrett

LML homepage:   http://www.olsusa.com/Users/Mkaye/maillist.html