You may wonder how the bronze sculpture you received was made and what the process is of making an exquisite bronze sculpture. We have many years of experience with bronze sculpture casting, so we will describe the whole process for you. We will use pictures of several bronze sculptures to explain all the steps.
1. Model Making
The very first step of bronze casting is to make an original model, which is always cast from clay. The clay model we make are always the best because we have the best clay masters. The shape of the finished bronze sculpture will be exactly the same as this original mold. Therefore, you can see the significance of creating this original clay model.
What we need to make the clay model are some pictures of the front, behind, left, right, and top view of the person to be sculpted. It would be great to include some videos that show the facial expression and demeanor. If not, several pictures of facial detail will work. These pictures help the clay master to create an accurate and exquisite clay model. Sometimes, we are asked to make 3D digital models from the photos our customers supply before our clay master has created the clay model. This could be helpful in some circumstances but may cost a higher price.
2. Plaster and Silica Sol Mold Replicating
After the original clay mold is completely dry, we move on to replicating the model with a plaster mold and a silica sol mold.
We put a layer of plaster on the outside of the clay model and then a layer of gauze on top of that. We repeat these two steps several times until we get a solid plaster mold. If the sculpture big, then we can divide the whole model into parts and make several plaster molds. Because bronze sculptures are often quite big, we do it this way frequently.
The inner surface of plaster mold is rough, and we need to make it smooth and soft, so we make another mold—the silica sol mold. Making silica sol mold is quite easy: just brush the silica sol on the inside of the plaster mold and wait for it to dry. When it is completely dry, we peel it off and are left with the silica sol mold. These two molds will be used to create a wax mold together.
3. Wax Mold Creating and Chasing
Once we have the outside, hard, solid plaster mold and the inside, soft, smooth silica sol mold, we can create the wax mold, which is important to bronze casting. We put the molds parts together and tie them up.
We pour hot melted wax into the molds and then gradually tilt and rotate it around. When the entire surface of the silica sol mold is covered with wax, we slowly pour out the excess melted wax. We wait until the first wax layer is totally dry and then repeat this step again several times until the thickness of wax mold is 4–6 mm.
After the wax is completely cooled, we remove the wax mold and trim it around the details. This wax mold will be as same as the final bronze sculpture, so we trim it carefully and make it exquisite. On the edge of the wax mold, we stick several wax strips to make a support frame, which is used as the gating system when pouring in the melted bronze. This wax mold constitutes the sprue system that will guide the inner flow of melted bronze.
4. Shell Making
In this step, we make a shell for the wax mold using the silica sol casting method, which is more advanced, so the bronze statue is higher quality when finished.
We prepare the silica sol solution and several different types of sand, starting with very fine sand and gradually increasing the coarseness of the sand for each layer. We completely soak both the inside and outside of the wax mold in the silica sol solution, and after the wax mold is covered, we submerge it in the finest sand for the first sand coat. When it is fully covered with sand, we let it dry completely. This step is done in a special room with air constantly blowing on the mold until the shell is totally dry.
When the first layer of the shell is dry, repeat the process with coarser sand. This step is repeated for 8–9 times, with coarser sand each time. We finish the 9th layer with the roughest sand. When it is totally dry, we proceed to the next step.
5. Melting Out the Wax
In the previous step, we made an exact shell by covering the wax mold. Now, we cut the shell carefully to make an opening in the wax strip’s side, careful not to cut the wrong place which will destroy all the work we have done so far.
We place the shell in a heated oven with the opening side facing down. The oven is heated to 1500 degrees Fahrenheit, at which temperature the wax in the shell will melt and flow out quickly. This protects the shell from cracking because if the oven is heated slowly, the wax will expand and the shell could easily crack. After the wax and steam drained out completely, we are left with a hollow, empty shell mold.
6. Bronze Casting
This shell is the mold into which we will pour the melted bronze. We melt down the bronze and affix the shell mold with the opening side up. If the shell mold is not completely dry, it could become very dangerous and explode when the bronze is poured in, so we need to confirm twice that there is no wax and no water in the shell. Once we confirm that the shell is dry, we pour the melted bronze into the shell mold very carefully because the liquid bronze is at a very high temperature. We then wait until it cools down.
Once the bronze has cooled, we gently hit the outside layer of the shell a hammer. After we remove of the sand shell, we can see the bronze sculpture, but now it looks black.
7. Statue Assembling, Welding, and Polishing
As we said, the statues are often divided into several parts. After we make all the bronze statue parts, we assemble them into one sculpture. Each part is connected by welding; this must be done very accurately because the shape of the whole sculpture is determined by its welding level.
With all parts welded together, we can see the shape of our bronze sculpture and proceed to the next step: polishing. The purpose of polishing is to smooth the welds and the surface of the sculpture. After polishing, we can see the original metal color of bronze.
8. Patina and Surface Waxing
A wide range of chemicals can cause patina on a bronze sculpture, which can turn the sculpture different colors. The most common colors are green and brown. We have the best sculptors who are very skilled with patina and can give the bronze sculpture the best, evenly-spread color.
A chemical solution is evenly sprayed on the bronze statue. Our sculptor roasts and sprays the chemical solution simultaneously. When this is finished, we cool the sculpture down and do the last step of bronze casting, which is surface waxing. This wax layer locks in the patina and protects the sculpture from fading.
9. Packing and Shipment
For us this lovely sculpture is perfect here but for our clients the sculpture has the last procedure to reach to them. We will wrap the bronze statue with white cloth for the first protection and inner packaging which will keep the bronze sculpture from dust and bump. The outer packing will be the steamed-wood or iron shelves which can support the well-packaged bronze sculptures and the filler inside.
Here are some project cases of our accomplished customized bronze sculpture art works.