Zach Gabbard, the owner and founder of Mission Foundry, is a man of many talents. He works the wax room, mold making, metal finishing, and casting. In the photo above, on the slab of yellow foam behind Zach, some small wax figures await preparation for casting. This preparation includes adding a wax funnel to the sculpture, as well as any additional wax supports, called sprues or gates, to help with the flow of bronze to all parts of the sculpture. I don’t have a photo of a wax sculpture with sprues but below are two seahorses with their funnel and sprues in bronze. (It made such an interesting object I kept it as cast).
The prepared wax sculpture is then dipped in a slurry, floured with dry silica powder, and hung to dry. In the two photos below, Zach is building up the mold on an architectural element that he will cast into bronze. The funnel is attached to the top of this cornice piece.
This process builds up a hard ceramic shell over the wax. It takes about a week to create a 3/8-inch shell in a series of nine dippings with drying time. The ceramic mold is fired at a low temperature to melt out the wax; then it is fired at 1500 degrees for about an hour to fuse the mold. Any residue from the wax vaporizes, the mold vitrifies (heats to a glass-like state), and glows a fiery red.
This is the moment to pour the melted bronze that has been heated in a furnace to about 2100 degrees into the mold. Once the bronze cools, the cast sculpture is ready to be removed from its hard ceramic shell. The only way to get the sculpture out is to completely break the shell, hammering first, and then picking out any ceramic pieces that remain. The last small particles of the shell are removed by sandblasting the bronze.
Metal finishing is next. The bronze sculpture still has the funnel with sprues attached. These have to be cut off, and the surface worked, so there is no sign of the supports. Think of freeing the bronzes seahorses from their poised equilibrium.
When a sculpture is cast in several parts like the Chalice I made for the Unitarian Universalist Church in Harvard, the pieces must be welded together.
The sculpture is now ready for a final sandblasting before its patina. The patina is the treatment on the surface, and the colors can range from black to green to a polished gold. The sculpture is heated with a blow torch, and a chemical or a combination of chemicals are brushed onto it. The reaction of the bronze with the heated chemicals oxidizes the surface and forms the patina. A coat of wax is added to protect it.
Now we have a finished sculpture, but no mold. That’s the rub. This process is called ‘Lost Wax.’ The sculpture is one-of-a-kind; and I cannot make another copy. If I had wanted to make an edition, that is several copies of the same piece, my original wax would have been used to make a rubber mold with a hard ceramic exterior encasing the rubber and giving it solidity. This rubber mold could then be used to make additional wax models of my sculpture. The process would then go to step one again – the wax preparation with a funnel and spruing, and dipping and flouring, to build up the hard shell for the bronze pouring. Every casting needs one wax model and a ceramic mold built up around it that will be destroyed in the process. To make several copies, you need to have a mold made from the original so you can make several wax copies.
For my small bronze figures, I go straight to casting from the wax without making a rubber mold. These pieces are cast solid and are one-of-a-kind. For larger pieces, the weight of the piece and the amount of bronze needed makes this direct casting impossible. By making a rubber mold, a wax positive of the sculpture can be created so that when the bronze is poured the final sculpture will be hollow. However, each wax copy made from the rubber mold needs to be retouched. A hand or seahorse tail might be distorted in the unmolding and either the artist or the foundry will need to touch up the wax. No two sculptures are ever exactly the same.
Zach is now casting Tree Harp for me. This sculpture has a two-part rubber mold; the wax parts will be cast separately and then put together. When I go to the foundry to see the completed wax, I will sign this one 3/6. This signifies that there will be 6 castings allowed and that this is the first. Once all the castings are produced, the rubber mold will be destroyed to prevent more copies of the sculpture. After Tree Harp is cast, I’ll apply the gold leaf in my studio and it will be ready to live permanently outdoors.
A great amount of work takes place in a foundry – the artisans working there are artists. At a large foundry, there will be workers who make molds and others who work only in wax. Many of them are sculptors, supporting themselves with a foundry job. Zach is just starting his foundry and does everything but the casting alone. I am so appreciative of his talents. When you enter the foundry door, there is a large sculpture — a wild vision of crazy sunflowers. It’s Zach’s work. I’ve already asked him to bring it to the farm for our outdoor sculpture exhibit this fall.