The Bronze Casting Process

The Lost Wax Process
Bronze objects have been created for over 6000 years. Craftsmen used bronze because it melted easily and hardened to a durable finish. Around 4000 years ago, artists in Mesopotamia began using the “lost wax” process to create larger, hollow castings. The “lost wax” process is still in use today.

Creating a bronze sculpture requires many steps. The artist of today first creates a model, typically in oil or water base clay. Rubber is applied to the surface of the model and a plaster “mother mold” is added to the rubber. The mold is made in multiple pieces and is then removed from the original model. The rubber and plaster mold is reassembled and filled with molten wax. The still liquid wax is poured out of the mold, leaving a thin wax shell. The rubber and plaster mold is disassembled and the wax pattern is removed. The surface of the wax is a copy of the original model, but will have some defects that must be touched up. A “sprue” system is added to the wax pattern. This creates a path for the metal to flow through.

applying plaster to a rubber mold

wax sprue system

pouring bronze into a ceramic mold

From here, the wax pattern is dipped into liquid ceramic slurry and then coated in sand. This step is repeated multiple times to create ceramic shell of sufficient thickness around and inside of the wax. The wax/shell is put into a kiln, heated to 1750° until all the wax has been melted out (thus "lost wax") and the ceramic shell is fired to a hard surface. While the ceramic mold is still hot, silicon bronze that has been heated to 2100° is poured into the hollow space. After the mold has cooled, the ceramic material is removed, the bronze sprues are cut off and the piece is ready for finishing.

It is important to note that in the US, most foundries use Silicon bronze. Silicon bronze is composed of 95.8% copper, 3.3% silicon, and 0.9% manganese. Silicon bronze is known for its easy pouring ability, lack of surface defects and superior corrosion resistant properties, even when submerged in liquids and chemicals. Foundries in China and other Eastern countries use a much lower quality bronze consisting of between 60-70% copper, often from recycled radiators and pipes. For quality castings, silicon bronze is by far the best and only choice for Carolina Bronze.

applying patina and torch to Ronald Reagan sculpture

Now the piece is ready for finishing. Multiple castings are usually needed to create one sculpture. These different sections of the original piece need to be welded together. The seams must be ground down and chased to recreate the original texture. Any pits or other defects in the surface must also be repaired and made to match the original surface.

Finally, the bronze sculpture is heated and chemicals are sprayed on the surface to create the “patina”, a colored finish. Several layers of wax are applied while the sculpture is warm to create a sheen on the surface and provide protection from the elements.

Each casting, even those in an edition, is a one of a kind, handcrafted work of art, created by highly trained artists and craftsmen. This, combined with the many hours of work involved in creating a sculpture, is why bronze sculpture can be expensive. Please keep in mind that each sculpture is unique, and as such, so is it's price. The cost for a basic mold, cast and finish job can range from a few thousand dollars for a 2' tall figure to ten's of thousands of dollars or more, depending on the size of the sculpture. That doesn't include the artist fee, cost of the base and any installation or engineering costs that might be required. For an estimate on your project, visit our "Estimates" page. Be sure to include accurate measurements, sizes, and photos to get an accurate cost estimate.