|Bronze Art casting process: Mold making, Lost Wax casting, Spruing and Gating, Ceramic Shell, Metal Casting, Chasing, Patina|
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Step 1: Artwork
Our staff artisans will study or create the sculpture and
make a determination on how the sculpture will be sectioned or
"laid up" for mold making. Complex molds will require the
original artwork to be cut into smaller manageable pieces. This
is, by far, the most critical step of the procedure. The detail
of the original must be captured and transferred in the mold, if
not, they will be difficult to replace in any other step.
Step 2: Molds
The sculpture is first sealed and then a release agent is
applied to allow for easy removal of the rubber mold. Depending
on the artist's requirements, we will create a silicone, latex,
or polyurethane mold.
Step 3: Wax Casting
The completed mold, having already been prepped, is now ready
for the wax. The mold is separated and the first coat of wax is
painted into the mold to capture all the fine details of the
artist's masterwork. The mold is put together and more wax is
poured in. It is then rotated until an even, thin coating is
achieved. Once it has cooled, a second coat is applied and
rotated to achieve a thickness of 3/16 to 1/4 of an inch. The
excess wax is poured out. After the wax has completely cooled,
the "mother mold" followed by the rubber mold is removed. Now
the wax casting is revealed.
Step 4: Wax Chasing
Seam lines are removed and the wax pieces are fitted for
alignment. Then the register marks are put in, followed by the
final wax inspection.
Step 5: Spruing and Gating
Wax rods are attached to the sculpture. These rods are called
sprus or gates. A large cup is attached at one end, this cup
will receive the molten bronze when poured. The placement of the
gate system allows molten bronze to flow through these areas
allowing gases to escape through smaller bars called vents.
Step 6: Ceramic Shell
We are now making a secondary mold. Though the materials are
much more modern, this serves the same function as mud did 5,000
years ago. We now dip the wax in a liquid binder solution. This
material is called "slurry" and a very fine
silica sand is
applied. Each coating is completely dried prior to the next. The
number of coats applied to a piece is determined by the size and
weight of the piece. The heavier the piece the thicker the shell
must be to support the metal. The slurry coats the inside and
outside of the wax allowing the sculpture to be hollow. The
chemical make-up of the slurry is monitored constantly to ensure
it's strength. The humidity and temperature of the slurry room
is controlled to allow for optimum dryness and hardness of the
Step 7: Metal Casting
The ceramic shell is
removed from the slurry room and placed in an autoclave or a
burn-out oven cup side down. A burn-out oven is simply a large
flame-heated oven, an autoclave is a large machine that heats up
under steam pressure. Either method will allow the shells to
de-wax. Once the shells are de-waxed, they are cooled and
inspected for cracking. Once again they are heated up to 1400
degrees and placed in the pouring pit. Bronze ingots are heated
from 1900 to 2100 degrees. The temperature that bronze is poured
is determined by each individual casting. The molten bronze is
then poured into the hollow shells and allowed to cool and
Step 8: Devesting
The shell material is now removed inside and out, and the unfinished bronze casting is revealed. It is then glass beaded, water or sand blasted to remove any remaining shell material from the intricate details of the casting.
Step 9: Welding
If the original was sectioned into multiple pieces, it would
now be carefully fitted and reassembled. A visual inspection is
done to check for any casting inclusions. If there are any
surface defects, these would also be repaired at this time. All
sections of the casting are welded together with great care and
attention to alignment.
Step 10: Metal Chasing
The sculpture is
polished to remove any sign of welding or casting defect and to
prepare the bronze for the patina (coloring process).
Step 11: Glass Beading
different polishing and detail tools are used without disturbing
the original texture of the sculpture. A final metal inspection
is performed at this stage of the process.
Step 12: Patination
The patina is the
finished color. Depending on the artist's preference, we may use
a variety of different chemicals which react to the metal to
achieve a certain look. Colors like: Museum Brown, Antique
Brown, Verde Green, and Gold Leaf are just a few we offer. After
the patina is applied, and depending on whether the artwork is
inside or outside, the sculpture is sealed with a wax coat
and/or lacquer to protect the finish. We offer hundreds of
Step 13: Crating & Shipping
is carefully and securely packaged in a wooden crate for safe
Step 14: Delivery & Installation
Delivery and installation of the final product completes the bronze art casting process.
There is no accurate record of when the lost
wax method of casting was first utilized.
It is believed the earliest users of the lost wax method began with a clay
core roughly the shape of the subject to be sculpted. This core was covered with
wax, and then sculpted to the finished form. Once the wax hardened it was
covered with clay. The object was baked, hardening the clay and melting the wax.
Because the wax method melted out the bottom of the baking receptacle or oven,
it was unusable or lost - hence the process is called "Lost Wax". The space
evacuated by the wax was then filled with molten bronze. Once the bronze cooled
and hardened, the clay was removed and the remaining bronze - cleaned and
Other names for the process include "lost mould," which recognizes that other materials besides wax can be used, including but not limited to: tallow, resin, tar, and textile; and "waste wax process" or "waste mould casting", because the mould is destroyed to unveil the cast item.
Casts can be made of the wax model itself, the direct
method; or of a wax copy of a model that need not be of wax.
Archeologists have found castings - thousands of years old. The basic principle of the process has remained unchanged, although many new techniques have been developed. The most significant of which was the use of molds from which many waxes could be made and the ceramic shell process gave a high quality casting.
Bronze was significant to any culture that encountered it.
It was one of the most innovative alloys of mankind. Tools, weapons, armor, and
various building materials like decorative tiles made of bronze were harder and
more durable than their stone and copper predecessors. Initially bronze was made
out of copper and arsenic to form arsenic bronze. It was only later that tin was
used, becoming the sole type of bronze in the late 3rd millennium BC. Tin bronze
was superior over arsenic bronze in that the alloying process itself could more
easily be controlled (as tin was available as a metal) and the alloy was
stronger and easier to cast. Also, unlike arsenic, tin is not toxic.
The earliest tin-alloy bronzes date to the late 4th
millennium BC in Susa and some ancient sites in Luristan and Mesopotamia.
Copper and tin ores are rarely found together (exceptions
include one ancient site in Thailand and one in Iran, so serious bronze work has
always involved trade. In Europe, the major source for tin was Great Britain's
deposits of ore in Cornwall. Phoenician traders visited Great Britain to trade
goods from the Mediterranean for tin.
Bronze is widely used for casting bronze sculptures. Many
common bronze alloys have the unusual and very desirable property of expanding
slightly just before they set, thus filling in the finest details of a mould.
Bronze parts are tough and typically used for bearings, clips, electrical
connectors and springs.
Bronze also has very little metal-on-metal friction, which
made it invaluable for the building of cannon where iron cannonballs would
otherwise stick in the barrel. It is still widely used today for springs,
bearings, bushings, automobile transmission pilot bearings, and similar
fittings, and is particularly common in the bearings of small electric
motors. Phosphor bronze is particularly suited to precision-grade bearings and
springs. It is also used in guitar and piano strings.
Bronze is typically 88% copper and 12% tin. Alpha bronze
consists of the alpha solid solution of tin in copper. Alpha bronze alloys of
4–5% tin are used to make coins, springs, turbines and blades.
Commercial bronze (otherwise known as brass) is 90% copper and 10% zinc, and contains no tin. It is stronger than copper and it has equivalent ductility. It is used for screws and wires.
Unlike steel, bronze struck against a hard surface will not
generate sparks, so it (along with beryllium copper) is used to
make hammers, mallets, wrenches and other durable tools to be used in explosive
atmospheres or in the presence of flammable vapors.
Indian Hindu artisans from the period of the Chola empire
in Tamil Nadu, used bronze to create intricate statutes via the lost wax method
with ornate detailing depicting the Gods of Hinduism mostly, but also the
lifestyle of the period. The art form survives to this day, with many silpis,
craftsmen, working in the areas of Swamimalai and Chennai.
In antiquity other cultures also produced works of high art
using bronze. For example: in Africa the bronze heads of the Kingdom of Benin,
in Europe; Grecian bronzes typically of figures from Greek mythology, in east
Asia; Chinese bronzes of the Shang and Zhou dynasty - more often ceremonial
vessels but including some figurine examples.
Bronze continues into modern times as one of the materials of select choice for monumental statuary.