Georgia Gerber - The Process
   
georgia gerber 
6790 heggenes rd 
clinton, wa 98236 
(360)341-6382 
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 Overview of the Bronze Casting Process 
         (Downloadable PDF Page 1    Page 2)

Nearly all of Georgia Gerber's work is produced at her own foundry,
utilizing the lost wax casting method. She learned the foundry process
during her college years at both the Bucknell University and
University of Washington Art Foundries.

Almost always the creation of bronze sculpture in multiples (editions) and producing one-of-a-kind pieces are accomplished in the same manner; the artist sculpts the form and a rubber mold is made from the sculpture. A wax replica is then cast from this mold, and this replica is in turn cast in bronze using the lost wax process, described below. For each sculpture in an edition, a new wax is cast from the rubber mold.

During her years in the Bucknell University Foundry Georgia and her professor, William Lazansky, developed an alternative approach to one-of-a-kind castings that precluded the need for making an expensive, labor-intensive rubber mold. Georgia and her crew have made further improvements to this system, adapting it especially to facilitate the casting of large-scale work. All of Georgia's unique public installations have been cast using this system. We know of no other foundries that use this approach.

The outline below illustrates this system. Note that many steps are the same as for the casting of multiple copies of a sculpture. For such edition pieces, each individual wax replica is sprayed with investment (similar to Step 3), and then treated essentially the same as unique pieces, beginning with Step 6.

 
From Clay to Bronze

Casting One-of-a-kind Bronze Sculpture in the Studio and Foundry of Georgia Gerber

Georgia SculptsStep 1
Georgia Sculpts in water-based clay
castable-sized piecesStep 2
The finished sculpture is sectioned into castable-sized pieces with thin metal shims.

Step 3

An "investment" made of sand, plaster, and vermiculite is applied to each section to a thickness of about 5 inches.
sculpture captured in plasterStep 4
Each section is removed and cleaned. There is now a negative imprint of each section of the sculpture captured in plaster.
wax is pressed against the negative imprintStep 5
A ¼" thickness of wax is pressed against the negative imprint.

plumbing network of waxStep 6
A "plumbing" network of wax (sprues and gates) is connected to the wax.

encased in a larger cylinder of investment materialStep 7
The entire section piece, with the pressed wax and sprue system attached, is encased in a larger cylinder of investment material - with part of the plumbing system protruding out of the top.
cylinder is placed upside down in a large kilnStep 8
The cylinder is placed upside down in a large kiln and heated with propane to 1,000°F for about 48 hours, which evacuates the wax (hence, the "lost wax" method"). This leaves a void inside the cylinder wherever there was wax. The negative plaster imprint imbedded inside the cylinder now has a ¼" void adjacent to its surface, connected to the voids left by the melted plumbing network. Since this network originally protruded out the top of the cylinder there is now a hole that provides access to all the voided spaces inside the cylinder.
bronze ingots are melted and poured into the hole in the top of the cylinderStep 9
The cylinders are placed right side up in a pit and surrounded by sand to re-enforce the molds as the metal is poured in.

Step 10

Bronze ingots are melted in a furnace to about 2,000°F and poured into the hole in the top of the cylinder. The molten metal flows through the plumbing system and fills the ¼" space against the negative plaster imprint, taking on the positive form. As it cools, the metal maintains this positive form, and so replicates that section of the original sculpture.
cylinders are broken open and the raw castings cleanedStep 11
After cooling, the cylinders are broken open and the raw castings cleaned. The plumbing system - now also replicated in bronze - is cut off to be recycled in the next melt.
individual cast sections are welded togetherStep 12
The individual cast sections are welded together, like pieces of a puzzle, to form the bronze replica of the original clay.
welding lines and other flaws are tooledStep 13
All welding lines and other flaws are tooled by skilled artisans to make a seamless bronze sculpture.
application of patina chemicalsStep 14
The final step is the application of patina chemicals - usually to a heated bronze - to get the coloration desired. Finally, a number of coats of wax are applied to seal and protect the finish.

foundry crew
Pouring Bronze

In the foundry there is a wide range of skills that are needed, from mold making to final finish. The Gerber Foundry has been fortunate to have a small, dedicated, and skilled staff of artisans who play an essential role in producing high quality bronzes.

In a small working foundry it has been important that each artisan become a sort of jack-of-all-trades, though each also has developed particular areas of expertise. No skill is more important, however, than the ability to do the final tooling. This is the phase in which all the welding lines and casting flaws are basically re-sculpted in bronze to match the original sculpture. This often means re-creating texture and form that has been lost due to the assembly process. On a large piece, this can be a significant task. This work requires incredible attention to detail, great skill with a range of tools, and above all an artistic sensibility that can recognize and replicate the artist's original intent. Virginia is a master at this crucial aspect of foundry work.


Virginia Keck has been working with Georgia almost from the beginning of the foundry in 1983. She displays her own sculpture at the Artisan's Co-Op Gallery in Langley, Washington. Besides tooling, Virginia is on the metal pouring crew and specializes in assembly of the large-scale work. She is a dancing enthusiast, and occasionally draws out the pattern of steps for new dances on the foundry floor.

 

 

Georgia's husband, Randy Hudson

Georgia's husband, Randy Hudson, runs the business end of things, makes molds, takes photos, pours waxes, does installations, shipping, and anything else that can get him out of the real work in the foundry - though he does pour the bronze. He claims that his two smartest moves in life were marrying Georgia and never learning how to weld. Randy is a concertina player and singer, and a member of two local music groups, "No Band Is an Island" and "The Rural Characters".

sculpting
Georgia sculpts almost every dayGeorgia sculpts almost every day. She usually works in "Idaho Buff" - a water-based clay commonly used for pottery. She likes the softness and fluidity of this material, which allow her to work quickly and expressively. It is common that she has two sculptures underway at any time - often a large commissioned piece and a smaller edition piece. She does not like to focus on one sculpture for too long at a sitting, and so moves back and forth between sculptures for fresh perspectives.

Georgia seldom draws or makes models before beginning a piece. Her ability to visualize in three dimensions lets her start right in by piling blocks of clay into the general form. Most sculptures, even the largest ones, are solid clay with minimal armature support. This gives Georgia flexibility in making changes as she proceeds.

Most sculptures start out quickly as she blocks out her vision in rough form. Even a large sculpture may be proportional and recognizable in only a couple of hours. However, from that stage until completion may take two weeks or two months, depending on how she feels about the piece. On the subject of completion, she is fond of saying "Much of art is knowing when to stop".

casting
The pouring of molten bronze is the intense centerpiece of the foundry experience. New metal ingots and recycled sprues and gates from previous castings are heated in a furnace by a mixture of propane and forced air to around 2000°F. The metal is contained in a silicon-carbide vessel known as a crucible, which can withstand the intense heat. The crucible we use holds 275 pounds of molten bronze. A typical pour day consists of melting three pots in succession to fill all the molds. We pour about every three to four weeks, depending on demand and the state of other work going on in the foundry.

casting - the pouring of molten bronze is the intense centerpiece of the foundry experienceThe heat of the metal is measured with a pyrometer, an electronic thermometer, submersed in the pot. When the correct heat is reached the crucible is plucked out of the furnace by a jib crane and hoist, which bears all the weight and allows access to the molds. A layer of debris, or slag, must be skimmed off the top of the melt before pouring.

Casting is a two-person job, with one person doing the actual pouring and the other stabilizing the holding shank and controlling the hoist to raise and lower the pot as needed. It is possible, though rare, to pour the metal so accurately into the cup hole of the mold that there is no spill over or splashing whatsoever. The occasional perfect pour is a celebrated event.

As the metal fills the mold it makes a sound that rises in pitch as it nears the top. This is always a welcome sign that indicates all has gone well. It is especially welcome if the pourer has gone ahead and started a mold with a questionable amount of metal left in the pot. Generally such gambles are not taken, but if a pour does come up short there is a good possibility it can be completed from the next melt, and the seam line that occurs can be repaired by welding.

patina
Georgia patinas most of her own sculpturesIn a strict sense the term "patina" refers to the thin layer of corrosion, usually brown or green, that appears on bronze as a result of natural or artificial oxidation. In the more general use of the term it refers to whatever finish a bronze sculpture ends up with. It is thought by some that the art of patination developed as an attempt to simulate the natural patinas found on ancient bronzes that were found buried or in sunken vessels. It may in fact have been that these bronzes were originally painted or colored in other ways, but the beauty of what nature had done to them encouraged "patinuers" to find ways to artificially cause such effects.

The most common way to patina a bronze is use a variety of chemicals to encourage oxidations of various colors. Generally, the brighter and more intense effects are achieved by heating the bronze first, and applying the chemicals by either brushing or spraying.

Georgia patinas most of her own sculptures. She uses three basic chemicals, which when combined in various strengths, application techniques, and differing heat levels can produce an astounding array of effects. Because any particular effect depends on many variables, individual patinas can vary somewhat from piece to piece even when attempting to replicate a particular look. This is why she tells clients that "You can order any patina you'd like, so long as you take the one you get." This is mostly in jest, because in reality it is usually possible to create a specific look, though it certainly is true that every piece will have its own unique charm.

The final step in finishing a bronze is the application of wax to the hot metal. Waxing with the metal hot and expanded makes for a durable finish that can be buffed to a high sheen once the metal cools. Periodic renewal of the wax will enhance the look of a sculpture and protect the stability of the patina. See Maintenance for more details.

mold making
mold making

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