Casting is the most primitive and also the simplest means of getting a metal or
metallic alloy into desired forms. Bronze appears to be the most extensively employed
material of all the sculptural media i.e. wood, stone, marble, terracotta, stainless
steel, iron, pewter, aluminum, silver or gold. Its great popularity is due primarily to
the many physical properties, such as structural strength, which allows a lighter, freer
and more open design for a statue, its great physical permanence and resistance to
atmospheric corrosion, ease of casting, and fine, compact surface, that can also take an
excellent finish or patina.
Bronze is basically composed of copper (around 85%) and other smaller quantities of
metals such as tin (4-13%), zinc (0,05-6%), lead (0,25-23%). The addition of more tin to
copper produces bronze and more zinc yields brass. Bronzes tend to have a warmer color
tone than brass.
In modeling a work in clay for eventual casting in bronze, the sculptor always takes
into account that the finished metal will be some what smaller than the original, due to
the shrinking of the hot melded metal, after it cools down. Another property of bronze,
which a sculptor should remember is that when it cools slowly becomes quite hard and
brittle. The opposite happens when is cooled quickly, after casting.
Very few sculptors nowadays cast their own statues even though the contemporary use of
bronze as a sculptural medium surpasses any previous use of the material. This is because
additional capital is required for expensive equipment, besides the capital for regular
studio facilities, the increased manpower needed for the reproduction of statues and the
many technical difficulties entailed in bronze casting. As a result many artists employ
professional bronze casters for the mechanical reproduction of their prototype statues.
The first step is for the artist to create the prototype sculpture with clay or
modeling modeling wax or any other material he is accustomed to. Then a mold is made of
the work by using silicone rubber (other rubberized materials could be used). A firm
external shell of plaster of Paris or fiberglass supports the rubber mould. After this
process, the mold is opened, cleaned, sprayed with a mould release agent and coated with
molten wax until a thickness of 4 - 10 mm of thickness (the bigger the statue the thicker
the wax). After the wax is hard, the mould is removed, and the replica is repaired of any
imperfections on the wax.
When this tedious work is finished, wax rods are attached on the wax replica, in such a
way, so that when the melded metal is pored, they will act as suppliers of metal and as
exhaust pipes for the gases produced, during the pour. At the main supply rod, we attach a
cup, in order to facilitate our pour.
When the wax assembly is finished, we cover it with a fire resistant mold, which will
serve as the receptor for the melted bronze. A new cost-effective method used mainly, by
the industry today, for high precision castings is the ceramic shell method.
A slurry, made up of calcined zircon flour and a binder (colloidal silica) is used to
dip the wax assembly. Then, it is covered with zircon sand (stucco) and let to dry. After
it dries, a second slurry is used consisting of molochide flour and binder. It is covered
again with stucco sand of molochide, this time. When dry, the second dipping process is
repeated 8-10 times. This is left to dry completely. All ends of the attached wax rods are
cut, so that when we place the mold produced in the furnace the wax melds and runs off it.
The wax remaining is burned out and we are left with a ceramic shell with no traces of wax
The next step is the pouring of the metal through the cup of the fire resistant mould.
When the metal sets, the ceramic shell is broken to free the cast bronze. The rods added
prior on the wax are now made of metal and are cut off. Sandblasting can be used to free
the bronze of any remaining ceramic. It is further finished with metallic brushes or
sandpaper. Many artists do not use finishing products of any kind, so that the texture of
the sculpture will remain unchanged.
Different chemicals produce the patina (coloration of the bronze). The bronze sculpture
is coated with lacquer or preferably bees wax in order to protect the patina from getting
affected by light and moisture.
Please contact the Artist for