[MR] Metalcasting from a positive master - expertise needed

[Sigrune at aol.com]

Is this a single sided casting like a medalion?

If so, something you could do is a multi-step process (very common)  First you would carve the design and make a "die" this could then be "stamped" into a matrix to make your mould.
I would recommend something like a fine grain clay/high temp plaster. I belive they now have some that will stand up to multiple castings without much breakdown.

The nice part of this style of casting, is A. you can create as many molds as you need/want, thus speading up the process considerably. (you are not waiting for the cast to cool before removal) and B. if you design your die corectly, you can have changeable inserts to make variations (date change, serial numbers, ect)

If you are looking to document it, this style is precicely the method used to make movable type.  In the process a iron or steel die was cut in the shape of the letter, it was then driven into annealed bronze or copper, the depth checked and that bronze piece would be affixed to be the "floor" of a mold for the type.

Depending on how large a cross section you are doing, it is possible a bronze/copper mold may serve your purpose, but it can be a real challenge to work steel that fine. With a clay/plaster base as your final mold, you could carve your positive into a block of resin, simply shove it in to get the impression.  I would avoid wax or soap for your master die, if you have very fine detail there is a chance that it will chip or peel off.

Hope this helps,
-Takeda Akimasa