I have used the material that dentist’s use for making impressions
for tooth crowns. Ask your dentist to get you the two part tubes, or
direct you for purchase…not cheap, but goes a long way.
Make a small box or unit to enclose the “putty”. Place the shell
pretty much down in the material, leaving an opening. Then, after
setting up, remove the shell carefully as not to rip the set up
"stuff", and fill the cavity with molten wax…let set up, carefully
"unfold" the material from the shell, sprue and cast. Very effective.
I have done tiny 1/2 inch or less cast in gold.
By the way, the shell will not burn out and leaves too much stuff in
the investment, and won’t give a casting.
This is fun, and addictive!!!
Rose Marie Christison