How To Make A Bronze Statue: 17 Steps for Lost-Wax Casting
Introduction to the Definitive Guide
Bronze statues are one of the most recognized art mediums in the world. The reason is they don’t lose value, they make beautiful decorations, and they are not easy to damage. Bronze sculptures can be made from various techniques. The most popular method is the Lost Wax Casting Process.
The Lost Wax Casting Process is an ancient and effective technique of making a Bronze Statue. With bronze articles dating back to over 6000 years. The lost wax casting process is also known as the Cire-perdue or investment casting. The long Wax Casting Process has been in existence since the 3rd Millennium BC. Although the technique remains the same, new technology and innovations have improved the process of making a perfect bronze statue. There are various methods and techniques for the lost wax casting process. The processes vary from foundry to foundry. The process of choosing the best Long Wax Casting Process can be a complicated process. A Quality “Lost Wax” bronze sculpture can withstand time. A bronze sculpture tells stories of past times, showing the culture and social structure of previous generations.
To make things simpler, I have written a rundown of definitive steps in the Long Wax Casting process.
Steps in the Lost Wax Casting Process for making a Quality Bronze Statue
Step 1 – Clay Mold
Artisans can apply the lost wax method to wire, stone, clay, plaster or metal and any other form of sculpture. An artist can use any of these materials and transform his idea into bronze. The first step in the lost wax casting is the molding of the model. I recommend using oil-based clay because it retains its softness and does not harden when exposed to air.
Step 2 – Plaster Mould
A plaster mold is formed around the original clay sculpture. This is carried out by coating it with various layers of either rubber or plaster. Around the plaster mold, another mold is coated made of plaster. The plaster is usually mixed with burlap to support the rubber. This plaster mold is the mother mold. Many sculptures are not molded in one-piece. Depending on the size of the sculpture, the layers of the statue would have to be molded. and several molds might be needed. After a while, the original clay sculpture is removed from them, and the mold is empty.
Step 3 – 4-6mm wall thickness Wax mold and chasing
The completed plaster mold is prepared, and molten wax is then poured into and out of the mold. To make a hollow replica of the original sculpture, it should need about three coats. This chasing process requires careful attention to form a workable mold. Uneven pouring or using a cold wax will cause the mold to pancake. Once it has cooled, a second coat is poured in and rotated to achieve an even wall thickness of 4-6mm”. The excess wax is removed out of the mold. After the molten wax has cooled, the “Mother plaster Mold” is removed followed by the rubber mold.
Chasing is the delicate process of cleaning the wax before casting by repairing imperfections and removing seam lines. The artist finally inspects the wax. He checks the integrity of the wax, and if the wax gets approved; the artist may sign the piece.
Step 4 – 7-9 layers of ceramic shell
The next step is spruing or gating. Here, channels through which the molten bronze will pass is attached to the wax version: a wax pouring cup, wax rods called sprus or gates, and air vents. The air vents release trapped air are all attached to the wax replica. These rods are channels used to direct the molten bronze into the piece. This allows the bronze to flow into the sculpture, depending on the size; a large cup is usually attached at one end.
This cup will collect the molten bronze when poured into the sculpture. This sophisticated system allows the molten bronze to flow through the wax replica. The channels also allow gases to escape through the air vents.
For the last 15 years, an innovation called ceramic shell has become the lost wax casting standard.
The ceramic shell also called an investment, is applied to each wax. This is carried out by dipping it into a heat resistant liquid, called “slurry,” The sculpture is covered with a heat resistant sand called “stucco.”
7-9 layers should be applied to the wax replica to achieve an even ceramic shell. Each layer must be allowed to dry completely before adding the next layer. The number of coats applied to the piece depends on the size and weight of the piece. The heavier the piece, the thicker the ceramic shell must be to support the bronze.
Step 5 – Heating and lost wax
When the ceramic shell covering the wax is completely dried, the sculpture is inverted. The statue is kept in a kiln at 1800℃ which bakes the silica. This causes the shell to become hard. The term” lost Wax” is derived from this temperature which all the wax melts and pours out of the shell.
Step 6 – Heat the ceramic shell to 1200℃
The ceramic shell is then placed back in the kiln and heated to 1200℃. This removes any leftover moisture. It also ensures the cast has a similar temperature to the molten bronze.
Step 7 – Melt bronze material
The bronze metal melts in a furnace till it reaches 1200 °C and turns molten. A huge graphite crucible, heated by a furnace, fills with the molten bronze. The molten bronze is put in the crucible to be poured in the shell.
Step 8 – Pour melted bronze into the empty ceramic shell
The empty ceramic shell has to have the same temperature as the molten bronze. This is to prevent the shell from shattering due to the difference in temperature. When the “pouring” begins, the graphite crucible is lifted out of the gas furnace. Afterward, the heated ceramic shells are brought out of the kiln to the pour point. Two artisans control the crane that holds the filled crucible in a “jacket.” The artisan with the control is the “lead pour.” The artisan that maintains the crucible balance is the “deadman.” A third artisan removes the dour and drags on the surface of the molten bronze. The molten pour into the large cup and down through the channels and sprues into the layers of the shell.
Step 9 – Place on the ground for 10 hours to cool the shell
Once the molten bronze fills the ceramic shell, it cools on the ground and left to solidify for 10 hours.
Step 10 – Remove the shell
The process of removing the shell is devesting. When the bronze has cooled, the sprues are removed. The ceramic shell breaks away from hammering and reveals the bronze casting. The bronze left in the sprues will be melted and reused, but the ceramic shell will be lost.
Step 11 – Sandblasting to remove all ceramic shells
After the shell is broken, the piece is then sandblasted, so the remaining ceramic shells are removed from the sculpture.
Step 12 – Welding
After sandblasting, any pieces that have been cast are merged back together. For example, if the original sculpture were separated into many parts, it would now be joined and reassembled. The final piece will look like the surface of the original sculpture.
If a base for the sculpture is needed, a custom cut and well-polished stone base are designed to carry the statue. The bronze sculpture is mounted on the unique base to enhance and display its beauty.
Step 13 – Polishing
The reworking of the bronze surface is called “metal chasing.” It usually takes many hours of labor. This removes signs that the sculpture has been through the casting process. Air bubbles, Imperfections or small holes are removed by filing the surface.
Step 14 – Repairing & Re-polishing
The artist re-examines the sculpture and checks for any signs of casting. If there are surface defects, these would also be repaired at the time. Each layer of the cast is welded together, giving attention to alignment. The artisan uses different polishing tools to prepare the bronze sculpture. Ensuring it is ready for the patina.
Step 15 – Patina
The next step is the “patina” – the coloring of the bronze sculpture. In ancient times, the Asians bury the bronze sculpture to oxidize the piece with nature. These days, oxidation takes only a few hours.
Patination is the process where different chemicals are applied to the bronze sculpture. This is to give it different colors and visual effects on its surface. Various chemicals create diverse colors on the bronze sculpture.
The three main chemicals that are used for patination are
#1. Potassium sulfide is for brown, gold and black
#2. Ferric nitrate is for red, golds and browns
#3. Copper nitrate is for blues and greens.
Various chemicals and mixes of chemicals are essential for patination.
There are also many ways to apply color to the bronze sculpture. The most used is the chemical application. Here, the “patina” is used by either spraying on or brushing on the bronze sculpture with or without heat. This is in several layers to achieve the desired color.
Step 16 – Surface Wax
A surface wax is applied to the sculpture before it cools completely. This gives the statue extra protection. The finished bronze sculpture is now left to cool completely.
After it cools, it should be clean with a soft polishing cloth. Another layer of wax is applied cold before it is dabbed again. This produces a polished shine on its smooth surface. The surface wax helps to enhance and preserve the color of the bronze.
Step 17 – Packing
Packing is as crucial as any other step in the lost wax casting process. The sculpture should be packaged in a custom made a wooden crate for safe shipping. The wooden box should be an ideal fit for the bronze piece. I recommend wrapping the sculpture in a bubble wrap and covering all open areas with duct tape. Covering the statue in a blanket protects the bronze from dust, the oil from human hands, grease, and moisture.
Since the era of the Bronze Age, humans have been obsessed with the desire for immortality. Many artisans put this desire in their art, so it is crucial for art to survive generations. Bronze Sculptures are timeless pieces. Each bronze sculpture is unique because of the complicated process it goes through. There are several techniques used in the lost wax casting process. Following the definite guide is essential to making a quality bronze sculpture.
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