What is lost wax casting？
Lost wax casting is also known as investment casting, method of Bronze(can be other metals) casting in which a molten Bronze is poured into a mold that has been created by a wax model, the wax model is melted and drained away and we get the bronze sculpture. To cast a model to bronze, first we made the negative mold from Clay sculpture , and the inside of this negative mold is brushed with melted wax to the desired thickness of the final bronze. After removal of the mold, the resultant wax shell is filled with a heat-resistant material, like silicon, plaster or sand, Depending on the heat-resistant material used they are called as Silica Sol Lost Wax Casting, Plaster mold casting and sand casting.
Lost wax casting progress
1：The Original Sculpture
First, we need an original sculpture. It is made either in clay, wax, wood, any material, also you can make it - Our sculptor and 3D technology can help you make it if you have a good idea, sketches or pictures.Our first job is to mold or create the original sculpture.This is a critical step of the procedure to capture the detail of the original. If this step is not carefully executed, critical details of the original will be difficult to replace in future steps.
2：Making the Mold
After the original sculpture is prepared, the mold maker applies the first coat of rubber. Once the rubber has set, additional coats are applied as required. When the last coat of rubber is set, a plaster shell is applied to reinforce the rubber during the wax pouring process.This is called a "mother mold". Most sculptures cannot be "molded" in one piece. For example, a sculpture with raised arms would require the arms to be molded separately. Depending on the original, several molds might be needed. The original clay is now removed from the mold. The mold is now empty. The empty mold is the first negative of the process.
3：Wax Casting（A Hollow Wax Replica）
Molten wax is poured into the mold，The mold is rotated until an even coating of wax is achieved. Once the wax has cooled, additional coats are applied until the wax achieves a minimum thickness of 1/8 of an inch. After the wax has cooled, both the “mother mold” and the rubber mold is removed revealing the wax casting, which is now an exact duplicate of the original piece.This process must be done smoothly and evenly so a workable mold is produced.
4：Spruing and Gating
For the wax replica to be used to cast, it must be "sprued" and "gated".Spruing and gating describe the process of attaching wax rods to the sculpture. A large cup is attached at one end, and it is this cup that receives the molten bronze when it’s poured. The gate system guide the molten bronze from the cup to the primary cavity, and also allow the air to be pushed out through vents.
The shell is actually a secondary mold. The wax is dipped in special ceramic-shell slurry, to which a very fine silica sand is applied. Each coat is allowed to completely dry before applying another coat. The number of coats required is determined by the size and weight of the piece – heavier pieces require a thicker shell to support the metal as it’s poured. The slurry coats both the inside and outside of the wax allowing the sculpture to be hollow.
The step creates a negative in the shell. The shell is placed into a burn-out oven, the wax inside the ceramic shell melts and pours out.This is where the “lost wax method” gets its name.
After the shells are de-waxed, they are cooled and inspected for cracking, and then they are heated up to 1400 degrees and placed in the pouring pit. molten bronze is poured into the cup and down through the sprues into the cavities of the shell. As the bronze cools, the last positive is created.
8：Finishing the Bronze Casting
- When the bronze has cooled, the shell is broken away to reveal the bronze casting，The casting is then glass beaded, water, or sand blasted to remove any remaining material from the shell that obscure the intricate details of the casting.
- Welding：If the original was sectioned into pieces, it’s now be carefully fitted and reassembled.Every section is welded together with paying close attention to alignment.
- Metal chasing： The process where all signs of welding or any other casting defect is removed to prepare the bronze for the patina
9：Patination - Coloring the Bronze
The final step is the "patina" - the coloring of the bronze.Patination is the process of applying various chemicals to the bronze to give it different colors and effects on its surface. There are three main chemicals that are used to produce the colors:
1. Potassium sulphide is used for golds, browns and black
2. Ferric nitrate is used for golds, reds and browns
3. Copper nitrate is used for greens and blues
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