I have two pieces of 1000 year old bronze pieces of jewelry
that I'd like to make exact replicas to wear.
First, you didn't mention the thickness nor area of the pieces, this
could make a difference in the molding technique, Generaly speaking,
RTV will give less shrinkage than a vulcanized mold, Castaldo makea
a Silicone called No-Shrink Pink that if donbe under extreemly close
temperature tolerance will give a near exact size wax pattern. they
also make a very good RTV putty that gives fair results regarding
Zero-D makes a very good RTV in a Liquid that has as far as I can
tell NO noticeable shrinkage, and Bill is a nice guy to deal with
and an Orchid member, as is Mr. Knight from Castaldo.
I use Zero-D's RTV to mold my CadCam waxes, and have had excelent
results, I have about 40 molds that I have done for one customer a
lot of the molds have had six to eight hundred waxes injected and
the detail is still good.
As far as attachiung a sprue, if you go with a liquid RTV then you
can cold fuse (sounds more professional than glue) the sprues to the
The Patina should not be affected by the RTV it would in the
Castaldo Pink under vulcanization, and you would have to solder your
Hope I've helped a bit,
Usual disclaimer, Not affiliated with either company just satisfied
customer of both