There are 2 different materials. one comes as sheets of “soft” rubber
that is cut and formed around the item to be molded and all is in a
metal frame and once “packed” it is compressed and heated in a
heating unit for what ever time period for the thickness of the mold.
The second way is using a catalyzed rubber (silicon or others)
material. Here the piece to be molded is again placed into some sort
of “frame” or containment unit, but since no heat is used with this
type of mold material, the frame does not need to be something that
withstands the high temperatures used in the first instance.
Then, with either material, there are a number of ways that the mold
can be developed. One way is to just pack the frame (vulcanized mold)
or pour the containment unit full of the catalyzed rubber. Going this
route, the resulting mold will have to be cut in such a way as to get
the original out of the mold and to allow a wax to be injected into
the mold and also easily removed.
With both types of mold materials, one can also “make” a separation
barrier where one wants the mold to separate. This method works
better on some forms than others but without seeing what is being
molded, I cannot say whether this would be a proper method for you
If the molds are filled with rubber, using either material type
discussed above, the mold will have to be cut to get the master out
and to get waxes out. Really good mold cutters are amazing to watch
when they can cut molds in ways you would NEVER believe, to get very
fragile waxes out of molds. Just writing this makes me recall some of
the molds I have seen that were truly something to see being cut. So
cutting molds of relatively simple pieces is “relatively” easy to
learn, but practice sure plays a huge role to do it “right”.
RTV (Room Temperature Vulcanizing) materials do not take heat to
catalyze/vulcanize so molds can be made of waxes and most anything.
Generally, but not always, RTV molds materials are softer than
vulcanized molds, and this can be an advantage and/or disadvantage,
just depending the piece and what you want and are used to using.
Hope this is a bit of help. If more questions please feel free to ask
and I will try to answer to the best of my ability. I am surprised
there have been no other comments on this, we shall see what others