Large model for reproduction

Jewelry Discussion
1

Hi all,

I have been asked to make a model which is larger than the kind of
things I am used to doing and I’m wondering if anyone has advice
about the best way to proceed. It is to be a vase of about 8 inches
in height and is meant to be the master for reproducing this piece in
bronze or brass. I’m wondering if wax is my friend here or maybe
clay? Or I could construct it in metal–maybe copper–

Do you make a really big mold for something like this or does it
have to be in two parts and then assembled?

Thank you, you brilliant Orchidians,
Janet

2

Hi, Janet.

I’d suggest you call these guys: artworksfoundry.com

They’ve been around a very long time. They’ll tell you the best way
to make your model, I’m sure. For those who are just curious about
the process, if Janet makes a metal model, she can just mold it and
get product from that. If she makes something in wax, that can be
cast and molded or cold molded, but I’m not so sure about that with a
large piece. Usually a clay model gets a ceramic mold put around it,
which is separated, the clay is scraped out, and the mold is cast
directly with metal. That’s traditional sculpture work, anyway. The
process of making a clay horse and getting it into bronze is pretty
involved, usually.

http://www.donivanandmaggiora.com

3

Janet,

I have turned wax models that are about 7 inches tall and around 3.5
inches in diameter.

The model is turned in three pieces from Ferris file a wax The
pieces are either wax welded together and cast or cast separately
and soldered together.

It sure would help if we had more info about what you want to do.

What is he diameter of the vase?

Reproducing a piece that big will be a problem except for a
production casting shop that is used to casting large items.

Will it have a design on it?

Will the model be used to make a reproduction mold? If it is molded
full size it will require a mold technique other that a hot mold or
RTV mold. I once made a two hot rubber molds of pieces that were
about 2.5 inches tall and 3.5 inches in diameter. What a problem
that was. I finally worked out the problems and cast 25 pieces of a
top and 25 pieces of the bottom of a piece of pottery and soldered
them together.

If you are interest in the wax turning process contact me off line
and I would be glad to help any way I can. I could prepare a paper
describing the process and show it on my blob.

I am going on a Thanksgiving trip to visit my daughters and may not
be able to answer any questions for about a week.

Lee Epperson,

4 
Do you make a really big mold for something like this or does it
have to be in two parts and then assembled?

Bronze can be cast in very large pieces and very complicated shapes.
The choice concerning one or two pieces, or more pieces would depend
on the design. Without knowing more proceed in one piece since it can
be divided later if needed. The caster will hopefully be a
professional and can provide the advice here. I think I would prefer
to model in the material I am most familiar with unless a specific
fact of the design favors a certain property.

Dan

5

I guess I missed the first inquiry on this but from what I have
picked up it is not a HUGE deal to make an RTV mold from a model
made of just about any material. Water clay, oil clay, plaster, soap,
wax, stone, paper, wood, etc. Once the mold is made, a wax is cast
and then the design of the piece will dictate how the piece is to be
cast. Today, most any LARGE bronze sculpture is cast in multiple
sections, usually not weighing over about 75 lbs in bronze, and
these pieces are welded together and the surface is chased back to
make an invisible connection. VERY complicated forms can be molded
and cast. If you want more please feel free to contact
me off list so as not to take up the time of disinterested folks here
on the list. I have a small one man foundry and cast mostly for my
wife’s work (http://www.MLCE.net) and for a few other artists. I am
happy to work with folks and will teach them any and all factors of
the process.

Hope this helps.
John Dach

6

The choice of materials for making a master model really depends on
the intended design and what you are comfortable with. If you’re
good at fabricating objects in metal and this is a simple fabricated
design, then copper might be the way to go. If it requires elaborate
sculpted detail that would be difficult to achieve in metal
directly, then wax or clay might work better - the choice of which
to use depends on what is easiest for you to work with. You could
also combine these media, using clay or wax applied over the copper
in certain areas. If you do decide to use clay, there are a range of
oil-based (Plasticine) clays available, which have some advantages
over water-based (potter’s) clay for this sort of project.

Oil clay doesn’t shrink or crack as it dries, and so it doesn’t mind
hav= ing rigid objects embedded in it. It comes in a range of
hardnesses and formulations, and can be softened with a little heat,
from a hair-dryer, for instance. Check with your mold-maker before
buying the clay - some of them, particularly the ones containing
sulphur, are antagonistic to certain mold rubbers. If you’re the one
who will be making the mold, test for compatibility with the rubber
you plan to use before investing a lot of time in making the model.

Do you make a really big mold for something like this or does it have
to be in two parts and then assembled?

Eight inches wouldn’t qualify as a sculptor’s idea of “really big”,
but I suppose it’s large for a jeweler. Most art bronze casting is
done by making rubber molds of a master model. Into this, wax is
poured, then poured out, leaving a relatively thin layer of wax on
the inside of the mold. This is removed, cleaned up, fitted with
gates and sprues for the metal to flow into and air to flow out,
encased in plaster-silica investmentor ceramic shell, then fired to
remove the wax entirely. Into the resulting void, metal is poured,
usually relying on gravity to fill it. (The centrifugal or vacuum
apparatus used by jewelers to cast metal isn’t necessary once there’s
enough metal melted to overcome surface tension.) You can make rubber
molds in one piece, cutting the rubber to remove the master, or you
can make rubber molds in two or more parts. The rubber inner mold is
usually supported by an outer “mother” mold in plaster or another
rigid material. Depending on the shape, this outer mold will have
one, two,or more parts that are assembled and held together with
rubber bands, clamps, or other fasteners. If you use plaster for the
outer mold, soak it in water before pouring the wax; this prevents
the wax from sticking to the plaster.

Andrew Werby
www.unitedartworks.com