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Lost-wax casting

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Lost-wax casting is a highly precise manufacturing process used to create metal duplicates of original sculptures. It is also known as investment casting, precision casting, or cire perdue, which is French for "lost wax."

Bronze casting by the Lost Wax Method
Bronze casting by the Lost Wax Method

This method allows artists to achieve incredible levels of detail in materials like gold, silver, brass, or bronze. Because the process relies on replacing a temporary material with a permanent one, it can capture very intricate shapes. Today, the term investment casting is often used when the process is applied in modern industrial settings.

The indirect method is a common way to perform this process through several distinct steps. First, an artist creates an original model using wax, clay, or other soft materials. Next, a mould is constructed around this model. This mould usually consists of a soft inner layer made of silicone, latex, or polyurethane rubber. A rigid outer mould, often made of plaster or fiberglass, supports this inner layer.

David Ascalon - Cast Bronze Sculpture Holocaust
David Ascalon - Cast Bronze Sculpture Holocaust

To ensure the mould fits together perfectly later, makers often use a shim with keys between the parts.

Once the mould is ready, the wax stage begins. Molten wax is poured into the inner mould and swished around to create a hollow coating. This coating is usually about 3 mm thick. After the wax hardens, the hollow copy is removed from the mould. The artist then performs "chasing," which involves using a heated metal tool to smooth out any marks left by the mould.

To prepare for the metal, the artist adds a "spruing" system. This is a tree-like structure of wax cylinders and a top "cup" that provides paths for molten metal to flow in and air to escape.

The next phase involves creating a ceramic shell mould. The sprued wax copy is dipped into a liquid silica slurry and then coated in a sand-like stucco. This process is repeated until a shell at least a half-inch thick covers the entire piece.

Purple Reigns
Purple Reigns

The piece is then placed in a kiln for "burnout." The heat hardens the silica and melts the wax, which runs out of the shell. This leaves only the negative space where the wax once lived. The shell is then tested for leaks or cracks before the final pouring.

To pour the metal, the shell is reheated in a kiln to remove moisture and prevent the shell from shattering due to temperature changes. The shell is placed in a sand-filled tub, and molten metal is poured from a crucible into the cup. Once the metal cools, the ceramic shell is hammered or sand-blasted away to reveal the rough casting.

Bronze casting by the Lost Wax Method
Bronze casting by the Lost Wax Method

Finally, the artist performs metal-chasing to file down air bubble pits and polish the surface until it matches the original model.

This technique has a very long history spanning thousands of years. The oldest known examples are gold artefacts from the Varna Necropolis in Bulgaria, dating to approximately 4550–4450 BC.

Grave offerings
Grave offerings

In the Indus Valley, a copper amulet from Mehrgarh dates to circa 4000 BC.

Dancing girl of Mohenjo-daro
Dancing girl of Mohenjo-daro

Other significant ancient finds include the Nahal Mishmar hoard in Israel, which contains copper objects from circa 3500 BC.

Hecht 090710 Sceptre
Hecht 090710 Sceptre

In Mesopotamia, Sumerian metalworkers were practicing this method by approximately 3200 BC.

Lost-wax casting is used in many specialized fields beyond traditional sculpture. In dentistry, it is used to create gold crowns and inlays, often using an alloy of 60% gold and 28% silver.

Purple Reigns
Purple Reigns

Some manufacturers use a "lost-foam" variation to make engine blocks by using polystyrene foam instead of wax. Artists also use the method to create glass sculptures by melting glass chunks into a heated mould. Even textiles have been used in the process, leaving fabric imprints on ancient gold ornaments found in Siberia and Viking Age brooches.

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🖼️ Images & Media (16)
File:Bronze casting by the Lost Wax Method.png
Bronze casting by the Lost Wax Method.png
File:David Ascalon - Cast Bronze Sculpture Holocaust.jpg
David Ascalon - Cast Bronze Sculpture...
The Process of Sculpture- From Clay to Bronze.webm
File:Purple Reigns.jpg
Purple Reigns.jpg
File:Grave offerings.jpg
Grave offerings.jpg
File:Hecht 090710 Sceptre.jpg
Hecht 090710 Sceptre.jpg
File:Dancing girl of Mohenjo-daro.jpg
Dancing girl of Mohenjo-daro.jpg
File:AT WORKSHOP.jpg
AT WORKSHOP.jpg
File:Wax forms for casting bronze statues.jpg
Wax forms for casting bronze statues.jpg
File:Bronze ornamental staff head, 9th century, Igbo-Ukwu.JPG
Bronze ornamental staff head, 9th...
File:Arte yoruba, nigeria, testa da ife, 12-15mo secolo.JPG
Arte yoruba, nigeria, testa da ife,...
File:TheraLateCyccladicIbex06656sq.JPG
TheraLateCyccladicIbex06656sq.JPG

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