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The Lost Wax Bronze Casting Process Explained
The “Lost Wax” bronze casting method dates back centuries to ancient Chinese, Indian, Greek and Egyptian cultures. And though the technique has evolved, it’s still much like it was in ancient times.
Bronze is the most popular metal for cast sculptures due to its strength, lack of brittleness, and expanding/shrinking properties throughout the casting process. Bronze alloys also allow for very detailed sculpting and a vibrant and colorful color and finish.
And then there’s durability: It’s been said that bronze sculpture will be the longest-lasting of all human creations. I find that humbling.
It all starts in the studio with an idea…then figuring out how to realize the vision in clay.
Step 1: Sculpting – Part 2
Once you have the piece largely together, you have to add a lot of finishing touches to get it ready for the next step. In the video below is my most recent piece, a bronze eagle sculpture called “Wind Chester”.
Step 2: Mold Making
Depending on the size and complexity of the piece, the original sculpture is coated with multiple layers of a liquid silicone mold material, which is then covered with a thick layer of plaster. Molds of larger pieces are made in sections.
Desk Buddy molds, being a little smaller, can be done in one piece. Each essentially creates a perfect negative image of a particular sculpture.
Step 3: Wax Pouring
At this point, hot wax is poured into the mold to create a solid wax piece. Each wax will later become a bronze.
Step 4: Wax Chasing
The waxes that come out of the mold are never perfect. Depending on how large and complex the design is, it might be cast in several wax pieces that have to be reassembled into a final design. As you can see with the rabbit sculpture below, the Desk Buddies are cast solid. They are small enough so we need only clean up the seam lines and any other little imperfections.
Step 5: Wax Spruing
At the foundry, the wax Desk Buddies have solid wax channels (called sprues and gates) attached through which molten bronze will flow.
Step 6: Shell Dipping
The wax Buddies are dipped repeatedly in a fluid ceramic material. This creates a thick, hard shell that will be tough enough to take the molten bronze.
Step 7: Bronze Pouring
The shell-encased wax is turned upside down and placed in an oven. The wax is melted out, flowing out through the sprues. Hence “lost wax” process! Molten bronze is then poured into the now-empty shell. The sprues added earlier allow the bronze to flow to every part of each section.
Check back for more steps as we complete them: Removing the shell, prepping and chasing the bronze, and applying the patina.
For another look at the lost wax casting method & process from beginning to end, please watch the following excellent video from the National Sculpture Society.