Rubber mold and an alternative

Agreed; if you have a very complicated piece of work, it is best to
send it out to a factory that has an expert mold cutter like Alan
Heugh. For those who do not have a vulcanizer and is in need of
making a mold for a simple project and do not have to make too many
reproductions…try the dental impression material. It is simple to
use; especially the 2 parts putty type. Just take equal amount of
putty, knead it for a minute or less…till the 2 separate colors
blend into one, slap it on to your project or lay the putty down and
press the model into it. It will harden in 3 minutes, remove the
model, pour wax into it and you got yourself a duplicate. If a 2
piece mold is required; with the model still in position, flip it
over, cut a few slots in it as key locks, knead a new batch of putty
and place firmly onto the backside. Another 3 minutes and you have a
2 piece mold. I make all of my symmetrical cuffs and ear rings this
way, by making only one wax pattern. I then make a putty mold of it
(no need of a metal model as in the case of a vulcanizer), pour 2 wax
duplicates for consistency and use those. For any big, high dome
type of ring with a back side cavity; I make a 4 or 5 piece mold.
Since the putty is not as flexible as the rubber mold, think like
playing with a 3D wooden jig saw puzzle. First fill the cavity
section( that is the inner top half of the ring) with at least 3mm
sticking out on both sides of the ring. Let it harden, pull it down
and out of the ring to check its release. Reinsert it, apply a very
thin film of baby powder to prevent the second part from sticking on
to it. Knead the inner bottom half, fill it in the inside , making
sure that this is also sticking out beyond the ring shank. After 3
minute, apply powder and make the outside half of the ring. This can
be a vertical half or a near horizontal half,depending on your
design. Cut some keylock slots. Apply powder then knead the other
exterior half. Another 3 minutes and then cut out the entry for the
wax injector nozzle.Remove model and start injecting. For brooch,
pendants, ear rings, I do not use an injector, just pour some wax
into one side of the mold, place the other half onto it and squash
out the excess wax. With this putty material it is easy take
impressions of various textured items, e.g. tree barks, fruits,nuts,
animal skins, minerals,etc. The dental impression material that I
use is made by G.C.(Japanese co.) and is called EXFINE. I have seen
G.C.'s wax products in American catalogs, so assume that it is
available. KERR has something similar, one half putty and the other
liquid…never tried it, so can’t comment on it. Min Azama in Tokyo
waiting for typhoon # 9 to strike and blow some of this heat away.