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HOW FINE
ART BRONZES ARE MADE
BRONZE:
an alloy of copper and tin which sometimes contains small amounts of other
elements, such as zinc and phosphorus. It is stronger and more durable then
brass, and has since antiquity been the metal most frequently used in cast
sculpture.
To become a successful sculptor in bronze, a sculptor has to become
familiar with the lost wax foundry process. Since most sculptors don't have
their own facilities, the original is brought to a large commercial foundry
specializing in fine art bronze casting.
To begin, a rubber mold is made of the original sculpture which is usually
made of oil based clay or wax. This "mother mold" is produced by
brushing on successive layers of thick rubber (silicone or latex) that,
when dry, is surrounded by a heavy application of plaster. When the plaster
dries, the "mother mold" is opened and the original is taken out
and destroyed. With a now hollow mother mold, the process continues. Hot,
liquid wax is poured into the mother mold to form a layer of wax of about
1/8 of an inch thick. After cooling, this wax is pulled from the mother
mold and is an exact positive of the original. Care is taken to
"chase" the wax replica; that is, to smooth out any discrepancies
that occur while pouring the wax. The wax chasing is integral to the final
outcome because how the wax looks at this stage will determine the final
look of the metal.
At this point, experienced foundry people will sprue the wax. There are the
gates and vents that the liquid metal will follow. Once the wax replica is
sprued, a series of dippings into a ceramic slury is applied. Each of the
six to eight layers of ceramic liquid is allowed to cure thoroughly. The
wax replica is now encased in a thick ceramic shell and placed in a burn
out oven. The oven is heated to 1,400 degrees Fahrenheit and the wax purged
from the shell. Thus the name lost wax process.
When both the metal and the now empty ceramic shell are ready, the molten
bronze is poured into the hollow shell and allowed to cool. Once cooled,
the brittle ceramic is carefully chipped off, concealing the metal inside.
After this, the bronze is sandblasted to remove any remaining pieces of
ceramic and prepare it for any metal "chasing". An experienced
metal "chaser" can then cut off the now metal sprues and weld any
imperfections. At this time any fabrication that is needed is done for
example such as reins on the bridle of a horse. After this, the bronze is
again sandblasted to prepare it for the final step.
The patination process is simply the quickening or colouring of the metal.
The bronze is heated with a torch to open the pores of the metal while
different chemicals are either sprayed or brushed on, which produce
different lustres and colours. Finally, the wax is brushed over the still
warm bronze and polished when cool to lock in their colors forever. The
bronze is then put on a wooden base and a name tag added. Sometimes granite
or marble is added as well.
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CARING FOR
BRONZE SCULPTURE
If you are fortunate enough to
own a bronze sculpture, there are a few things you ought to know in order
to properly maintain and protect it so that it will retain it's beauty and
value.
Unfortunately, moisture and chemicals in the air affect bronze, and
although outdoor sculpture is more susceptible to these factors, it is
really only a matter of time before your indoor sculpture will begin to
show signs of weathering as well. Bronze, and the paint like finish often
applied to bronze; referred to as a "patina"; loses it's sheen,
and even undergoes changes in colour, when exposed to impurities in the
air.
Luckily, caring for your bronze sculpture is really quite simple. For
indoor sculpture, regular dusting is a must, followed occasionally with a
coat of wax. It it is an outdoor sculpture; you will need to clean it with
a mild detergent and thoroughly rinse it before applying a coat of wax.
There are several products readily available: Cinstantine Wax, Johnson
& Johnson Paste Wax, and Butcher Wax are three used successfully. One
coat of wax is all that is necessary, and it should be rubbed down to a
thin layer. I use an old pair of nylons to polish with but be careful not
to polish to hard and rub the finish off. A thin coat is preferable to a
thick one as dust can collect between the layers of a thick wax coat,
causing the wax to smear and gum up. A thin application of wax is more
attractive and more water repellent, and creates a smoother finish. You can
expect to apply a coat of wax at least once a year for an outdoor bronze,
and about every eighteeen months for inside sculpture. Just remember that
when the piece begins to look dull, it's time for another application.
Bronze restoration is still in it's infancy as a craft. However, much
progress has been made in application and technique thanks to the combined
efforts of chemists, artists, conservators, and art historians. Should your
sculpture need a repair or if you need to have it appraised to determine
age and value you can consult your local museum's conservation department,
a professional restorer (most often found through trade publications or
recommended by a museum or gallery>, or you can contact a bronze
foundry.
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DISPLAYING YOUR SCULPTURE
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check back.
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Commissions are welcome.
Check out my new page coming soon on memorial plaques, custom urns and garden
memorials.
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