The Lost Wax Casting Process

Lost wax, or the cire-perdue process, is the traditional method of bronze casting. The method has been around for roughly 4,000 years and was used by the early Egyptians, Greeks, Africans and masters of the Italian Renaissance. Today bronze is still used to create coins, statues, decorative articles and much more. Small bronze coins can be found in pockets and cash registers around the world.

Despite the technology explosion of today, the lost wax method of sculpture and art object duplication has changed very little since its inception. The anticipated result of the process is to be able to duplicate an item for marketing in multiples rather than a single item. The process is quite straightforward, but each step must be adhered to with sharp attention to detail.

The first step in the lost wax sculpture/art object duplication is to create in either wax or special sculptor's clay a master item. For the sake of explanation, we will call the project in this piece a sculpture. While creating the original, it is wise to consider the undercuts (areas that go under limbs for instance) and open areas inside the shape. These will require additional vents and access for your casting material to enter and exit.

Once the original is refined and ready for duplication, flexible molds must be made of the original. To continue, place a layer of clay around the entire sculpture. Around the layer of clay, build a support mold of plaster. The plaster coating is put on with sleeves between all pieces so that it will come off in sections. This enables a three-dimensional item to be replicated. When the plaster is dry, it is removed; the clay is taken out and the plaster shell is replaced. The void between the sculpture and the plaster is where the flexible rubber is poured. The plaster is removed, the rubber is cut open and the original sculpture is released. The rubber mold is set back into the plaster shell, where it is ready for the wax to be poured.

Melted wax is poured into the mold and left for a couple of minutes. This short time creates a thin cast of the sculpture. Excess wax is poured away and recycled into another pouring. After the wax cast is cool, its hollow shape can be removed. Hollow casts are made because they are easier to manage, less costly and do not warp like solid, thick bronze items often do.

Any flaws, such as pinholes, obvious sectional marks, etc., are removed (chased). A network of vents and branches are added. These channel the metal flow and eliminate air pockets. The entire package is dipped into a slurry of thin ceramic clay. Sand is applied to this layer while wet and is then left to dry in a special climate-controlled environment. Eight to ten layers such as this are added to insure proper support for what will be the metal casting.

The slurry-coated wax figure is placed in a burnout oven and heated to about 1800 degrees. This does two things: burns out the wax and hardens the shell. It is now ready for liquid metal. Bronze is melted (at around 2000 degrees) and poured into the hot slurry shell. Upon cooling, the shell is cracked, chipped and sandblasted away to reveal an exact duplicate of the wax figure.

All vents and branches that are also cast in bronze at the same time the sculpture is being created are cut away. Any unevenness or seams, lumps, etc., are chased (cleaned). If any parts of the sculpture had to be removed during the casting process, they are now welded back on. If a bronze base is made, it is now attached, and the entire item is grounded and tooled with high RPM air tools to smooth all uneven areas. One final sandblast is done and the piece is ready for a patina. Several colors might be combined for the desired effect, and they are applied by dipping, pouring or dripping onto the bronze. When heated with a torch, the chemicals change the surface color of the metal and become more permanent. A sealer of some sort of wax is used and is most often applied with a brush and torched. After a final polish, the piece is completed.

Foundries often offer tours or allow visits during the shell, casting and finishing processes. Find a receptive foundry owner and take a first-hand look at a seldom seen and not truly appreciated craftsman at work.

Note: For each and every duplicate casting produced, a new wax model is poured and the whole procedure must be repeated. Weeks of work are involved in each reproduction, and each is an original made from its own wax model. Because of the subtle nuances of the process, no two are exactly alike.