Lost-wax casting

Lost-wax casting is used in jewelry-making to create precise and detailed metal pieces using wax and heat.

What is lost-wax casting? #

Lost-wax casting (also called investment casting or the lost wax method) is a technique that turns a wax model into a metal piece. The wax is surrounded by a refractory mold, removed with heat, and molten metal is poured into the cavity it leaves.

Also known as lost-wax casting, it is widely used in jewelry-making to create precise and detailed metal pieces. In this process, a wax model of the desired piece is created. Then, the wax model is placed in a mold and heated to remove the wax. Next, the molten metal is poured into the mold, and once cooled, the jewelry piece is extracted.

Basic steps of lost-wax casting: #

A provisional wax model is crafted, following the design conceived by the artist. The wax can be easily molded, and intricate details can be added or removed.

• The wax model is surrounded by a refractory material layer, such as clay or plaster, which solidifies to form the mold. Small holes are left for the wax to escape and the molten metal to enter.
• The mold is heated in an oven, causing the wax to melt and flow out through the holes, leaving a cavity with the exact shape of the model. Hence the name “lost-wax.”
• The molten metal is injected into the cavity of the mold, taking the precise form of the model. The metal used can be copper, bronze, gold, or other materials.
• The metal is allowed to cool, and then the mold is broken to extract the metal figure. The final finishing touches are added, such as polishing, chiseling, or patination of the surface.

This technique allows great freedom in designing the desired shapes, and it has been used to manufacture ornamental objects such as jewelry, statues, masks, and more.

Making the wax for this technique: #

To make the wax for this technique, materials like beeswax, paraffin, polymer clay, or other malleable substances that can be easily molded are used.

Wax for replicas #

Silicone or rubber molds can also be used to reproduce an original metal piece and obtain wax replicas through injection. The wax must have an appropriate thickness to prevent it from breaking during demolding or cracking during heating.

History of lost-wax casting #

Lost-wax casting is a metallurgical technique used to obtain metal figures, typically in bronze and gold, by creating a mold from a prototype modeled in wax or another material.

This technique was developed independently and simultaneously in different regions of the world, such as Mesopotamia, India, China, Mesoamerica, and the Andes, from the 3rd millennium BCE to the 16th century CE. Each culture gave its own style and purpose to the metal objects created with this technique, including jewelry, ornaments, utensils, weapons, or religious sculptures. In America, it seems to have originated in Colombia around 1000 BCE.

The Florentine Codex, a 16th-century document that records the history and culture of the Aztecs, contains illustrations depicting the lost-wax casting process in Mesoamerica. Indigenous painters represented the various stages of metal object production, from raw material preparation to the final finish.

In Japan, the lost-wax casting technique is known as rokushō and dates back to the Yayoi period around 200 BCE. The most famous piece made with this technique is the bronze statue of Buddha in the Todaiji temple in Nara, which stands over 15 meters tall and weighs more than 500 tons.

Lost wax casting process in 8 steps #

1. Wax model: carved by hand or injected into a rubber mold (see wax).
2. Tree: several waxes are attached to a stem with sprues.
3. Investment: the tree is placed in a flask and covered with refractory plaster, which is de-gassed to remove bubbles.
4. Burnout: the flask goes into the kiln and the wax melts and burns away, up to about 700 °C.
5. Casting: molten metal enters the cavity by centrifugal or vacuum casting.
6. Quenching: the hot flask is dipped in water and the plaster crumbles.
7. Cutting and cleaning: the sprues are cut and the piece is pickled.
8. Finishing: it is filed, polished and, if it has stones, set.

Materials and tools #

• Jewelry wax and spatulas.
• Refractory investment and flasks.
• Burnout kiln.
• Crucible, tongs and torch.
• Centrifugal or vacuum casting machine.
• Protective equipment.

Advantages and limitations #

• It reproduces very fine detail and complex shapes.
• It allows several copies of the same model.
• It works for gold, silver, bronze and platinum.
• It needs several stages and equipment; the mold is used only once.

Lost wax method compared with other casting techniques #

Common casting defects #

Frequently asked questions #

Why is it called lost wax? Because the wax of the model melts and disappears from the mold: it is “lost” to make room for the metal.

Which metals are cast with the lost wax technique? Gold, silver, bronze, brass, platinum and others, depending on the kiln and crucible.

Can it be done at home? With suitable equipment and safety precautions it is possible on a small scale; molten metal and plaster call for care (workshop safety).

How long does it take? Between half a day and a whole day, counting preparation, burnout and finishing.