Metal Working: How Is A Brass Sculpture Made?

A wax object is made and coated with clay. The wax is melted away, leaving a cavity into which the sculptor pours molten brass.

The art of brass and bronze sculpture-making is thousands of years old. Several early civilizations made brass or bronze sculptures. Brass is an alloy of copper and zinc. Bronze is an alloy of copper and tin. Modern sculptors use different combinations of copper, tin, zinc, lead, or other metals in an alloy to make brass sculptures. There are two current methods for making brass sculptures: sand-casting and "cire perdue" or the lost-wax method.

The lost-wax method is the traditional sculpting method followed my most current sculptors. The first step in this process is to create a wax object that looks exactly like what the final sculpture should look like. Sculptors often warm the wax and use various tools to work the object into its final shape.

After the wax image is finished, different sculptors coat it in different ways. The most common method is to work an unfired clay mold around the wax. Other sculptors use a fire-resistant plaster or even powdered mud. At least one or two holes should be left in the coating in order for the wax to escape.



Then the mold is ready to be fired in an oven or kiln. During this process, which may take up to twenty-four hours, the outside clay or plaster coating hardens, and the inner wax melts and runs out of the holes or ports left in the outer coating.

When the clay/plaster mold cools, the hollow inside area is shaped exactly like the outside of the wax object. The next step is to heat and mix the copper and zinc alloy until it is molten. This alloy's melting point is around 2000 degrees Fahrenheit, so special materials and extreme caution must be used for the heating and pouring. The molten brass is poured into the clay mold and then allowed to cool.

The final step in the lost-wax method is to break the clay mold away from the outside of the finished sculpture. The solid brass sculpture is now finished unless the sculptor wishes to polish it or apply any finishing touches to it. With the lost-wax method, no two sculptures are alike since the mold is broken during the process.

The second way to make a brass sculpture is the sand-casting method. This method is common for industrial brass-making. In this method, a mold is made from a special sand/clay material that is packed around the model. Then the encased mold is enclosed in a steel frame. The two halves of the steel frame fit together tightly. The molten brass is poured into the mold, and after the brass cools, the steel frame is disassembled, and the sculpture is removed. With this method, it is usually necessary to rework the sculpture, sanding off the lines left by the seams of the steel frame. The sand-casting method allows multiple sculptures to be made almost identically.

Whichever casting method is used, the final brass sculpture may have dark brown brass tones, or it may have a light coloration or "patina." The patina is usually blue or green, though blue patinas may age to appear verdigris, or green-gray. The green coloration is caused by the copper in the casting. Various chemical washes can be applied to the outside of a sculpture in order to impart various patinas. Brass won't rust outside, and salt water doesn't seem to affect it, so brass sculptures should stay beautiful for many, many years.

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