September 30, 2008 on 8:15 pm

Last week, I wrote about the process used to create our pewter recognition awards. This week, I will write about the process used to create our bronze recognition awards. As with our pewter recognition awards, the same basic process is used both for our existing recognition awards, as well as the custom awards we create specifically for our customers.

The bronze casting process used to create our unique awards is called the “lost wax” casting process, and it has been around for thousands of years. It involves a few more steps than the pewter casting process described last week.

As with the pewter award production process, the first step involves the artist creating a model of the award design, usually using clay. In the case of an inventoried recognition awards, this creation is based solely on the artist’s inspiration. In the case of our unique custom awards, this design is driven by the spec of a specific customers.

Once the model has been created (and approved by the customer, in the case of custom awards), a mold is made. This mold is created by coating liquefied rubber around the original model. Before coating, the rubber is heated to a near-liquid form so it is easy to apply to the model. The rubber is then allowed to cool, and as it cools it hardens. Once the rubber mold has fully cooled and solidified, it is cut in half, and the original model is removed. The mold now contains a cavity that has the same dimensions as the original award model.

The next step is to heat wax up until it is in liquid form. This molten wax is then poured into the cavity of the mold. It is then allowed to cool and harden. Once it has solidified, the now-solid rubber mold is removed, and you now have a wax model that is in the same exact form as the original clay model.

The wax is then cleaned up of any imperfections, pits, excess wax material, etc. Once it has been cleaned, wax “sprue lines” are attached the wax. These are like tree branches that create channels or conduits to the wax sculpture award. These sprue channels provide access for the molten bronze once it is poured, and allow air to escape when the bronze is poured, so air pockets and pits don’t develop in the bronze sculpture award. These sprue lines all converge into a wax cup at the top of the sculpture award. This cup will be the entry point where the bronze will be poured.

Once the spue lines have been attached, the entire wax structure is dipped into a slurry, which contains liquid silica, a cement- or ceramic-like material. The wax sculpture award is removed from the slurry, and the shell is allowed to dry and harden. Once it is hard, the sculpture is then re-dipped, then hung for hardening. This cycle repeats until a shell of a sufficient thickness has been created. The larger the sculpture award, the thicker the shell.

Once the shell has been created, the entire structure is placed cup-down in a kiln, which serves two purposes: 1) it further hardens the ceramic shell, and 2) it melts the wax, which then flows out of the sculpture. This is why the process is called “lost wax” casting. Now, all the remains of the original sculpture award is a cavity inside the ceramic shell – again, in the exact same shape as the original model, with the addition of the sprue lines and cup that were created.

Next, bronze ingots are placed in a crucible, which is then heated in a furnace. Once the bronze is melted to a liquid form, it is poured into the cavity that exists in the ceramic shell. As the bronze cools, it hardens. Once it is fully solid, the ceramic shell is broken away from the bronze sculpture award. You are now left with a bronze sculpture award that is in the same form as the original model.

Finally, the sprue lines and excess metal are trimmed from the sculpture award, and the metal is polished to a smooth finish. In some cases, patina is applied, which colors the metal. The core sculpture award is now complete!

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