Bronze sculpture has been created by the lost wax process for thousands of years, and although modern machinery and techniques make the process a bit faster and easier, the essentials are still the same.
It starts, for me, with a spark of an idea flickering in my head, which over a period of time - weeks, months, or sometimes even years - gradually reveals itself to me until it is dancing inside my eyelids. Then I get out the clay. I don't draw, so I do not work out details in advance on paper. Instead, the figure develops as I work directly in the clay or wax. Although I sometimes create my models out of sculpture wax, stoneware ceramic, or stone, I usually use an oil-based clay designed for sculptors. Creating the clay original, changing shapes or positions as they evolve, refining the details, may take weeks or often months.
When the model is finally completed, I next make a flexible silicone rubber mold so that the model can be reproduced in wax. Most sculptors take their models to professional mold makers for this. In 1985, when I was starting to do bronzes, I was quoted hundreds of dollars to make a small - and what I thought was simple - mold. After I got over my shock, I asked a lot of questions, bought a bucket of mold material (about $100 per gallon), and made the mold myself. It may take from a day to a week, depending on the complexity of the model, to make the flexible molds for the wax within the range in which I currently work. Often the clay or wax original ends up distorted or destroyed by the mold-making process.
After the mold has been completed, stripped off the model, and cleaned, molten sculpture wax is poured into it. If the sculpture is not very thick, the wax - and therefore the bronze - might be cast solid. If it is bulky, the wax - and the bronze - must be made hollow. The molten wax is poured into the mold, sloshed around, poured back out, and the mold allowed to cool. This process is repeated until a layer of wax 1/4 to 3/8 of an inch is built up inside the mold. When the wax is cold, the mold is carefully stripped off the wax.
The wax is cleaned and chased: mold marks are removed, air bubbles and other imperfections are filled in, details sharpened up or sometimes added in the wax. If the sculpture is made from two or more different wax pieces, they are joined together and cleaned. This wax work can take hours or days, depending on how good the mold is and how detailed or complex the sculpture is. Each piece of sculpture to be cast requires a separate wax. After the wax has been cleaned and detailed, I take it to the foundry.
The foundry usually takes four to six weeks to do the casting. Sprues and vents -wax rods and wires to make channels for the flow of the bronze- are added at the foundry. The wax is repeatedly dipped into a silicone slurry, coated with a silicone ceramic powder and dried until a shell 1/2 to 1 inch thick has been built up around the wax. If the sculpture is to be hollow, the wax is cut apart to expose the inside as well as the outside to the slurry. When the shell is finally finished, it goes into the furnace where the wax is melted out - the lost wax method. When the wax has been burned out clean, molten bronze is poured into the now hollow shell. After the bronze cools, the shell is broken apart to release the new bronze. The sprues and vents, which are now bronze rods and wires attached to the sculpture, are cut off, and the piece is sandblasted to clean off all residue from the shell. If the bronze was cast in pieces, they are now welded together with bronze rod. Now I get the sculpture back from the foundry.
Once, when I was younger and had fewer injuries, I dreamed of casting my own sculptures. But the reality is that a foundry needs many thousands of dollars worth of equipment and a minimum of three workers. Good foundry work requires not only knowledge and technique, but also experience, strength, and stamina. At this point in my life I prefer to concentrate on the creative aspects of my work.
When I get the casting back, there are metal stubs where the sprues and vents were cut off. I grind these off, and clean up any surface bubbles or flashings. If a vent was in the hair or other detailed area, I restore the details with burrs, punches, chisels, or other tools. (See photo at top.) The bottom is ground flat, and if a base is to be attached, I drill and tap the bronze to accept screws. When all the chasing and cleaning is done, I work all the skin surfaces to a bright surface with steel wool or "scotch-brite" pads so that the finished patina will glow.
Patination is a chemical reaction that both colors and protects the bronze. The chemicals may be applied cold or hot; they may be sprayed ,brushed, dipped, or fumed. Some develop the color immediately while others may take days or weeks. I use primarily hot patinas, either sprayed or brushed. I heat the bronze with a torch, spray or brush the patina on in a thin layer, then rub back the highlights with steel wool. I repeat this process several times until I get the depth of color I want. Because I like color I often use several different patinas on the same piece for additional color. When the patina is finished, I add the sterling parts to those sculptures which get them, then heat the piece gently and apply paste wax. When it cools, I hand buff the sculpture, then wax and buff it again. If the sculpture is on a base, it gets screwed on at this time. I make the wooden part of the base and order the marble made to my specifications. Felt is glued to the bottom, then I sign and number the finished bronze.
So far, the original model was destroyed making the mold for the wax, the wax was destroyed making the shell mold, and the shell was destroyed to get the bronze casting out. Working in bronze demands both an ability to let go and a trust that everything will come out all right in the end. And the final result is a piece of art that can last for thousands of years.
© 1995, 2000 C Whitehorn