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Process overview
This section broadly describes the bronze casting
process. It basically consists of making a negative mold from your wax
original sculpture and to pour molten metal in that mold to make a
positive reproduction of your original
The lost wax technique involves constructing a shell
around a wax sculpture. The shell is only about a half a centimetre
thick.(3/8”). When dry, the shell is placed on a suspended grill and
heated with a strong gas torch. The wax will melt out of the shell and
drip out to be collected into a pan under the grill, the wax is “lost”,
leaving a thermal resistant ceramic mold in which you can later pour
molten metal. When the metal has frozen inside the mold, the shell is
broken off to reveal the bronze sculpture, a metal reproduction of your
“lost” wax original sculpture.
First you
will be making a wax sculpture. This picture represents a green wax
model but not all waxes are green.
We have used a female torso as an example but you can choose any
other form. For the purpose of this exercise it must be a fairly
bulky shape, with no part thinner than 1cm (0.4”) A complex form
with thin appendages requires some advanced casting techniques
beyond the scope of this manual. It must be no larger than 10cm (4”)
in any direction.
A solid block 10X10 cm (4’’X4’’) would probably
the maximum you can attempt here. |
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“Sprueing”
This diagram
shows the wax sculpture to which a wax “sprue” and a wax cup have
been attached. The sprue is the channel through which the metal will
eventually enter the empty mold.
The sprue is fairly narrow; to make it easier to
pour molten metal inside such a small opening, a funnel shaped cup
has also been attached. This whole structure will be encased in a
ceramic shell
The sprue or sprues, vents and pouring cup
constitute the “feeding system”
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| “Shelling-up”
A slurry of ceramic and
silica is mixed and painted over the entire structure (cup, sprue
and sculpture). Ceramic sand is sprinkled over the wet slurry to
make the layer thicker. Several coats are needed to make the shell
about half a centimetre thick. (3/8”). It is then left to dry for a
day or two.
This thin shell is resistant to thermal shock yet
porous enough to allow gases to pass through its walls when the
molten metal is poured into it.
This is why we call this the “thin ceramic shell”
technique. A thicker shell would not be as porous and would require
the sculptor to create “vents” to allow the gases to escape. With a
thin shell we can, in most cases, get by without constructing any
venting system. |
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“De-waxing” or
“Burn-out”
Once the shell is dry it can be placed over a metal grill and heated
with a strong gas torch until the wax melts out completely, leaving
an empty shell. The melted wax can be collected in a pot under the
grill. The wax can then be reused for another project. In that sense
it is not lost but you have indeed lost your original wax shape,
hence the label “lost wax technique”.
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| Melting and pouring
With our simple and inexpensive
temporary furnace, you will need about half an hour to melt the required
amount of bronze metal. When the metal is molten, you will pick up the
crucible out of the furnace with a pair of tongs and gently pour it into
the ceramic shell that has previously been set up nearby.
Done! Just
wait for the metal to cool. |
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“Knocking-off”
The shell is left to cool down for
several hours until it can be touched. The shell is then broken off by
hammering it gently until the bronze sculpture is freed. The sculpture
is further cleaned with a wire brush.
The ceramic mold is therefore a one off mold that is
being destroyed during the process and can only be used once. If you
want to cast more than one copy of a particular piece, you must have a
mean to make a new wax and repeat the process. This is explained in the
“Taking it further” section of the manual.
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“Chasing”
The sprue and the “button” (the metal was
poured to fill the entire shell, including the cup, which now looks like
a “button”.) must be cut off. This can be done with a hack saw or with
an angle grinder equipped with a metal cutting disk.
Small imperfections are smoothed out and the entire
piece is sanded clean and shiny, ready for patina.
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By proceeding you acknowledge having read and
understood our
Terms and
conditions
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The
tutorial will not have you establishing a complete backyard foundry.
The furnace is a temporary, fold away furnace and most tools and
equipment can be found in DIY enthusiast’s workshops or garden
sheds. |
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This practical project will not
show you more advanced casting techniques such as hollow casting.
However, such topics are treated in later chapters of the manual.
Here is the
table of contents. |
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Even though this is a fairly safe
process, there is always some risk involved in working with power
tools, flames, gas cylinders and molten metal. Necessary health and
safety precautions will be clearly labelled throughout the manual. |
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We endeavour to keep the project’s
cost to a minimum and show you how to save money. |
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All measurements are expressed in
both metric and US customary units. Pricing indications are
expressed in US dollars. |
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After having completed this simple
project, you will be familiar with the basic principle of bronze
casting and the manual gives some further advice and guidance on how
to take it further, use more advanced casting techniques and how to set up your own small scale art
foundry. |
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Other
tutorials by Bodyscape.
Body Casting Manual
A complete body casting instruction manual explaining in details how
to make a realistic, life size and very elegant plaster sculpture of
someone’s torso (or any other body part.)
Available in PDF or in print.
Mold Making Manual
An illustrated tutorial for artists, sculptors and hobbyists
demonstrating the principles of mold making using a variety of
methods and materials.
(Coming soon.)
Contact me with a expression of interest. |
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Soap and candle message board
A community message board for soap making, candle making and other crafts. Join today and share recipes, ideas and meet new friends. |
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