One of the most noticeable things in a cemetery is a gravemarker. They are designed as a personalized way to remember a loved one. While most gravemarkers are granite and marble carved with the departed’s information, some include elaborate designs and even statues. Some of the most common gravemarkers are ornamental statues cast in bronze.
For centuries, bronze has been the most popular metal used for casting. Whether an artist uses bronze to cast large pieces, life-size pieces, or they use it for casting sculptures to be placed with gravemarkers; it’s a versatile metal that continues to stand the test of time.
What is Bronze Casting?
Bronze casting means molten bronze is poured into a hollow mold or form to create original bronze sculptures or other objects. Sculptors use many methods in bronze casting, including the lost-wax process, ceramic mold, and sand pit casting. All of which have been successfully used for centuries to make everything from small and large sculptures, weapons, tools, medals, and more.
But, you may be wondering how bronze sculptures are made. In this article, we’ll explore the art and craftsmanship of casting in bronze and the many methods used to this day. But first, let’s look at the history of bronze during the ages.
A Brief History of the Bronze Sculpture
The Beginning of Bronze
- Humans started using bronze around 5,000 years ago; an era called the Bronze Age.
- Bronze was initially used for tools and weapons, but it soon became material for art.
Classical Greek and Roman Age
- The Greeks produced thousands of bronze pieces between c. 700 BCE and c. 100 BCE.
- Most of this work did not survive since many pieces were melted down and used to make other sculptures or tools.
- The earliest Greek bronze sculptures were crude reliefs. Artists made reliefs by hammering flat sheets of bronze over each other to form the image.
- They made the first life-sized images from bronze during this time.
Medieval Age
- The popularity of bronze sculpture started to decline due to Early Christianity’s doctrinal opposition to monumental sculpture. Instead, the church enlisted the services of artists to create small ivory carvings and crucifixes.
- The Romanesque period (1000 AD) saw a revival of sorts as more ornamental pieces were being created again, like the Brunswick Lion in 1166.
Renaissance Age
- Although marble was the main focus of sculpture during the Renaissance (1400-1600), bronze sculpture once again surfaced in Europe.
- Artists studied the bronze work of civilizations from Greece and Rome and attempted to recreate them.
Mannerist Age
- During the 1500-1600s, many upper-class families in Europe started collecting and commissioning pieces such as monumental sculptures for grand public spaces and items for their lavish homes.
- The most famous Mannerist bronze sculpture was Benvenuto Cellini’s (1500-1571) Perseus with the Head of Medusa. He made the piece to clearly show off the fine details and form of bronze casting, making it obvious it could compare to the much-appreciated and life-like work created from marble.
Baroque Age
- Baroque sculpture of the 1600s took sculpting to new dynamic and dramatic heights surpassing the craftsmanship of the earlier Mannerist and Renaissance works. Artists recreated many copies of original marble works in bronze.
- Many artists, such as Giambologna, would reproduce bronze copies of his original marble and stone works and create original works in bronze.
Neoclassical Age
- Large installation public pieces were made to honor historical figures and military heroes.
- Sculptors also crafted smaller decorative bronze works during this period (the 1700s) for collectors. These pieces included clocks and even furniture.
19th Century
- More monumental pieces were made during this time, such as Carlo Marochetti’s bronze statue of Richard the Lionheart situated outside the Houses of Parliament in London.
- Smaller decorative works, including clocks and furniture, continued to be made. These items became so popular that manufacturers established bronze foundries.
- The foundries reproduced replicas of famous stone or marble works for the public to purchase.
Modern Age
- One of the most famous bronze pieces from this era (the 1900s) was Auguste Rodin’s ‘The Thinker,’ which signaled the modern age of bronze work.
- Many abstract and surrealist pieces also included the use of bronze.
In recent times, sculptors and manufacturers are taking a more modern approach to the casting process. They are using silicone mold material and doing home location metal casting. However, the original ancient process of metal casting remains pretty much the same. Let’s look at the more popular ways to cast molten metal bronze.
Bronze Casting
Bronze is the most popular metal used for casting. It is versatile, and the process is relatively easy. Bronze expands in the mold as it is cast, resulting in a more detailed statue or sculpture. However, it also shrinks as it cools, making removing the finished piece from the mold a breeze.
Since bronze is a copper-based metal and its melting point is much lower than other metals, you can use bronze to cast other items, such as weapons, musical instruments, mechanical parts, and much more. It is also a durable metal that resists corrosion making it popular for outdoor bronze statues and art.
Ancient civilizations created some of the earliest known bronze sculptures around 2,500 BCE. People of ancient Greece, Africa, China, and India used early bronze objects such as weapons and tools. For many of these ancient cultures, bronze was essential as a way of life and used in ceremonies, decoration, and military.
The Bronze Casting Process
The casting of liquid bronze is a versatile process that uses different molds and works with different materials to create various items.
The National Museum of Ireland features many items from the bronze age that show how this liquid metal revolutionized great civilizations throughout history and set the stage for future applications of this metal.
Let’s take a look at the different bronze casting processes and methods.
Lost Wax Casting Bronze
Originally called “cire perdue” in the middle ages, the lost wax casting is one of the more effective ways to make a bronze sculpture.
The entire process involves building a ceramic mold around an original sculpture carved in wax. This wax sculpture is then sacrificed when you pour the molten bronze into the mold. This process is also called “lost wax.”
As the hot liquid metal dissolves the wax, it pours out of the mold allowing the bronze to fill in the gaps left behind, creating all of the details of the sculpture. As soon as the bronze cools, the sculptor can remove the finished bronze piece from the original mold. Let’s look at a modern way to do the lost wax casting process.
Rubber and Silicone Molds Used in the Lost Wax Casting Process
Another way to create a lost wax sculpture is using a silicone or rubber mold. You first carve a clay sculpture, and once it is finished, you pour a layer of silicone rubber over it.
The liquid nature of the silicone finds its way into all of the fine details of the clay sculpture. A thick plaster layer is applied on top of the silicone when the silicone is cured. This layer creates what is called a “mother” mold.
Seams are added so the mold can be separated into two halves, but also allow for tubes (sprues) in which you can pour the wax into the mold. As the plaster dries, the two halves are split open, and you peel the rubber mold off. The next step is to clean any remaining pieces of the clay original stuck in the rubber out.
Once the rubber is clean and dry, put the pieces back together, and pour hot wax into the sprues. This creates a thin layer inside the mold called a wax pattern. This wax pattern will be removed from the silicone when cooled and cleaned to remove any blemishes, bubbles, or seam lines.
The sprues on the wax pattern will look like rods attached to the item to be cast. These sprues will be the spots for pouring molten metal into but also create air vents to release any trapped air as the metal is poured. Many choose to use silicon to make the wax pattern because they can use it repeatedly to make multiple copies.
Ceramic Shell or Investment Casting
Now that you have created your wax pattern from either carving it or pouring it into a silicone mold, an investment or ceramic shell is applied all over it.
To do this, the wax piece is dipped into a heat-resistant liquid and then coated 6 to 12 times with stucco or sand for extra heat resistance. These layers protect the wax as you slowly form the ceramic shell around it. This shell will be used as the final negative for the bronze cast.
Once the ceramic shell coating the wax is dry, the piece is turned upside down and placed into a kiln at 1800 degrees. This high temperature causes the shell to harden and become strong, and the heat melts the wax inside. As the melted or lost-wax pours out, the shell is ready for bronze casting.
You would then place the empty ceramic shell with the pouring cup or opening to the mold inside facing up. You pour the molten bronze into the cup, which makes its way down into the shell cavities. When the bronze has cooled, a positive is made.
Sand Casting Bronze
Sand casting is a one-object style process that uses a resin-bonded sand mold to make simple items like flanges, discs, and gears. When the resin-bonded sand mold is fully cured, the sculptor begins pouring molten bronze from a pouring cup into the sand mold. After the bronze cools, you remove the cast item from the mold.
Sculpting Large Bronze Pieces
Casting a large sculpture such as a monumental sculpture or garden statue is a lengthy process. The artist typically works from a smaller scale model in clay, plaster, or wax to create the details for the final larger finished project.
When they are satisfied with the small-scale sculpture, they’ll begin planning the structural support logistics for the larger sculpture. They will start sculpting the large sculpture using clay, wax, or plaster on these supports.
If the sculpture is large, the artist may need to cast the final sculpture in pieces and then weld them together later.
Chasing & Finishing
Chasing is the process of removing any seams or imperfections created from the wax, plaster, or clay original sculpture before casting the bronze sculpture. Since the surface texture of a bronze cast is so detailed, all tiny marks on the final mold will show on the positive cast sculpture.
If there are any imperfections in their clay or wax original sculpture, the artist will use heated soldering irons, heat guns, and other tools to eliminate them. The artist removes them at this stage because removing them from the final cooled bronze statue is much more difficult.
Once the final bronze sculpture is cast and cooled, the mold is opened up, and the final touches to finish the piece can begin. First, the metal sprues, or the large diameter tubes pouring the bronze into the mold, are cut off. You then sand the sprues down until you achieve the desired finished surface.
If more work is needed, the artist may sand-blast the surface of the bronze sculpture to further remove any oxide oils or inconsistencies in the finished piece. They may even use a wire brush or other texturizing tools to even out the surface.
Patina
You may have heard of the term “patina” but not know what it refers to. When a sculpture has a patina, those chemical compounds provide a protective coating on the sculpture’s surface, preventing corrosion. Before a patina is applied, the sculpture’s surface is free of any oils left by the wax or clay sculpt so that it fully penetrates the bronze.
Many artists use this process to protect the bronze’s surface and for esthetic reasons. Some of those reasons may be to adjust the color or texture of the final bronze sculpture.
Bronze Casting FAQs
Is Bronze Good to Sculpt With?
Bronze makes an excellent metal for sculptures because it can create great details and is easy to use. It is also a very strong and durable metal that doesn’t break easily if extra work is needed, such as sanding or grinding to finish the sculpture.
As bronze gets cooler inside the mold, it contracts. This makes it easy to remove the bronze object from the mold. If you want to add a patina to the metal after it comes out of the mold, bronze is very versatile and can be finished with the appearance of silver or gold.
Is It Easy Cast Bronze at Home?
If you want to start bronze casting, it is recommended that you work with a professional casting studio instructor first. Casting in bronze requires special and costly equipment. Before you purchase your casting setup, knowing how to use the equipment properly through a class is essential for safety and keeping initial costs low.
Is It Expensive To Cast Bronze Sculptures?
Yes! Casting bronze is a time and labor-consuming process. Although bronze is a cheaper metal to work with, it takes a lot of time to make even the smallest single bronze sculpture.
Taking classes, purchasing a studio setup, and getting the necessary tools, can be expensive. However, over time these costs will pay for themselves with each piece you make and sell.
What Temperature is Needed to Make Molten Bronze?
The melting point for bronze will vary depending on its alloy composition. Bronze is mostly 90% copper; the remaining 10% comprises tin, nickel, aluminum, or zinc.
The average melting point of bronze is approximately between 1700-1900F. It is best to preheat the molds to stop the molten bronze alloys from cooling too quickly until a cast is made.
Conclusion
Even though casting bronze is an ancient art, it is still practiced today for many practical and artistic reasons. Whether an artist uses bronze to form an outdoor piece of art or a decorative piece for a memorial marker, the versatile and universal nature of bronze makes it one of the most preferred metals for casting.