How Are Bronze Sculptures Made?

Bronze has, for hundreds of years, been favoured by artists as the ideal medium for sculpture. Its versatility, durability, its rich colour possibilities, as well as its ability to achieve the finest of details and of course it’s beautiful finish, all make this medium pretty much perfect, for fine art sculpture. 

Over the years many have asked me… “How are bronze sculptures made?” 

Let me take a stab at explaining the process.

First of all, all bronze pieces are casts, not carved or chiselled. 

There are many different bronze alloys, but typically modern bronze is a blend of  88% copper and 12% tin.  Bronze has been used for thousands of years.

It's been used to create tools, weapons, and in many industrial applications. But of most importance, of course, its used for monumental statues, sculptures, reliefs, statuettes and figurines. 

So to put it simply, a bronze sculpture, is a three-dimensional piece of art made by pouring molten (metal) bronze, into a mould, allow it to cool and harden, then de-moulding it, to reveal the bronze cast replica of the original artwork.

😳  Explaining that succinctly and in one sentence was quite challenging. 😂

First the artist creates their masterpiece in whatever material they work with, typically clay, water or oil based, plaster or some artist work directly with wax, eliminating the step that follows.

A mould is created of the original, usually consisting of a flexible polyurethane rubber with a stiff plaster shell. This is created to produce a wax cast of the original.

The process called the ‘Lost Wax Process’… Here’s why.

Melted wax is now brushed on or poured into to the mould, which is an exact negative of the original, the mould is twisted an turned, rotated so that the wax coats the entire inner surface, till the desired thickness of about 3/16" of wax is achieved.  

After the wax hardens and the mould is removed. The artist will now re-examine the wax cast very carefully and corrects any flaws, repair any air bubbles and remove any seam lines created by the mould. This is known to as 'wax chasing', a crucial step as the final bronze will be an exactly duplicate this wax model.

Wax bars and tubes are now attached to the sculpture, to provide pathways for pouring the molten bronze during casting. Vents and Gates are also attached to aid the metal flow and to allow trapped gases a path to escape. 

All the wax becomes negative space during the process, which will ultimately be replaced by Bronze.

Now it's time to create the 'ceramic shell.' This is achieved by repeatedly dipping the entire structure into a vat of liquid slurry and then into a bed of silica sand. This is repeated about 9 -10 times. A hard shell about ½” thick forms around the wax. This is know as the “Investment.” 

When dry the shell is then inverted and placed into a kiln where the wax melts away, and runs out via the vents, wax bars and tubes leaving a negative space.

Now it's time for the bronze...

A large graphite crucible, fired in a furnace to 1700ºF, filled with molten bronze is ready. The ceramic shell is also heated to approximately 1100°F to ensure that the bronze flows freely throughout the entire sculpture.

The “Dance of the Pour” begins... Molten metal is poured into the investment and you new born bronze sculpture is created.

Approximately one hour after the pour, the piece is now cool enough to handle. With hammers and power chisels the ceramic shell / investment is broken away from the solidified metal. The vents and gates are also removed.   

The piece is then sandblasted to remove any remaining segments of the ceramic shell from the bronze. When clean, the sculpture advances to the metal shop…

The piece must be inspected again carefully and all imperfections repaired.

The bronze is now as exact replica of the artist original sculpture.

Now let's apply some colour or patina to this masterpiece... Through the application of various chemicals brushed in and heated into the metal with a touch gun, we attain our desired colour and effect.

The final step is putting a thin coat of clear wax over the bronze to enhance and preserve the patina.

As you can see, creating a bronze sculpture is a very detailed and complicated process.

I hope now through a clearer understanding of the process, we all develop a deeper appreciation of a bronze sculpture.

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