WELCOME TO THE FOUNDRY
We invite you to explore and learn about our process here at
Michael Hall's Studio Foundry. We hope to facilitate an inspiring and fulfilling experience for our clients and guests, as we continue to share our knowledge and skill in producing museum quality bronze sculptures since 1975.
Watch the preparation and execution of a bronze pour in the following video..
The Art and Dance of a Bronze Pour
Watch the creation of a bronze sculpture from conception to completion in this next video..
Read on to learn more about the production of bronze sculptures..
~ART IN THE MAKING~
THE CREATION OF A BRONZE SCULPTURE BY USE OF THE TRADITIONAL LOST WAX, CERAMIC SHELL, CASTING PROCESS
In the sculptor's studio, the finishing touches are applied to the original sculpture. With artistic lines and accurate interpretation this sculpture, honoring the medical profession, is now ready for an amazing and complicated series of events which will culminate in a richly patined, beautifully conceived and executed work of fine art.
MOLDS FOR THE MASTERS
THE ART OF MAKING REPLICATION MOLDS
The original sculpture may initially be created in a wide variety of materials including: plasticine (an oil-based clay), terra cotta or stoneware (water-based clay, wet or dry), plaster, wood or wax. These different mediums allow the artist to create the unique texture varieties throughout his or her collections of fine art.
The lost wax process, also referred to as cire perdue, requires first the careful engineering of a quality mold made from the original sculpture. This flexible rubber mold is used to create a hollow wax copy of the original, which is eventually “lost” at last to be replaced with molten bronze. Rubber molds, most commonly made from different types of cold molding compounds activated by catalyzers, can be brushed or poured onto the surface of the original.
These rubber mold sections are supported by a plaster casing, called the “mother mold”, allowing the flexible rubber mold to be held rigid enough and in perfect form for the wax pouring stage of the process.
The complex network of rubber sections are keyed, all components bound together within the mother mold, and sealed for pouring.
This rubber mold is used each time the artist desires to create another copy of the sculpture. The series, or reproductions of an original work of art, is termed an edition.
THE WAX CASTING
UNDERSTAND YOUR WAX
The new mold is now ready for creating a hollow wax positive, capturing in fingerprint detail the exact work originally sculpted. This, and every wax, will ultimately be lost in the “burn out” part of the process. Studio Foundry makes and uses a specially formulated pattern casting wax which is heated and carefully poured into the mold.
The mold is gently rotated to insure an even coating, always being mindful of surface bubble elimination, and then the wax is poured out.
The wax may also be brushed into the open mold for the first coat, after which the mold sections are then closed and bound for additional wax pourings. Several wax pours at specific temperatures are necessary to develop the required wall thickness of the wax sculpture, approximately one eighth inch, which must be relatively uniform to insure a good metal pour. If the wax is not consistent thinner areas will inhibit the smooth flow of the molten bronze, resulting in unseen weaknesses in the final cast, or even an unusable casting due to voids.
REPLICATING SCULPTING IN WAX
The wax is then given enough time in the undisturbed mold to cool, after which it can be carefully removed from the rubber mold. Chasing, a term which means to clean and re-sculpt, is done twice, once in the wax and again when the sculpture is in bronze. Wax chasing is done with heated metal spatulas, knives and assorted wax sculpting tools, allowing the wax chaser to remove any flashings or irregular fins of excess material, which may have seeped into tiny gaps between seams.
Spru and vent joins are areas on the sculpture, where the molten wax has been channeled to fill the sculpture and where vents have been designed in the mold to allow trapped air to escape as the wax is being poured. These areas must also be chased off the sculpture, along with all other undesired surface irregularities such as tiny bubbles, which must be filled and retextured. The wax pouring and chasing specialists at Studio Foundry are all artists, highly skilled in resurfacing the sculpture to the exact requirements of the client, often referring to the original art piece to be certain of the utmost detail. Finally, the artist is often called in to give his or her approval and the process continues.
SPRUING and GATING
SPRUING FOR A BETTER TOMORROW
When the wax copy of the original sculpture meets the exacting requirements of the artist and foundry, a wax spru system is designed with a pouring cup, gates, and vents all attached to the perfect wax. Gates are systematically positioned along the wax to channel molten bronze into the casting mold, and vents are engineered to relieve air pressure inside the mold to insure a smooth flow of metal into every recess as the sculpture becomes bronze.
INVESTMENT CASTING MOLD
FINGERPRINT DETAIL THROUGH CERAMIC SHELL
During the investment process ceramic shell is built up around the gated and vented wax sculpture, leaving the pouring cup and vents open at the top, until the whole assembly is sufficiently thick enough to contain the weight of the molten bronze. The ceramic shell investment material, applied by repeated dipping, begins with a colloidal silica slurry. When wet with this slurry, dried silica is stuccoed over the entire surface by means of a rainfall or fluidized sanding system. Depending on the size and weight of the whole wax assembly, numerous coats are applied (usually about eight) in alternating layers of slurry and stucco. The final application may be reinforced with stainless steel mesh in areas where additional strength is determined necessary.
THE WAX IS LOST
Now the casting mold is complete and requires removal of the wax within to make way for the sculpture to be poured in metal. The entire casting assembly, called a tree, is then flash fired as it is placed in the burnout kiln, which has been preheated to 1900 degrees Fahrenheit. This high temperature serves both to fuse the ceramic shell and to burn out the wax entirely, including the volatilization of any carbon remaining from burned wax. Thusly, we now have a perfectly clean and very strong ceramic shell casting mold.
MOLTEN BRONZE AND THE MOMENT OF TRUTH
The wax burnout leaves a hollow mold, completely devoid of wax and ready to accept the molten bronze. After close examination for any cracks, and patching if necessary, the ceramic shell mold is returned to the kiln and brought up to approximately 1400 degrees Fahrenheit. At Studio Foundry, this is a time of reverence and concentration. The work of art has been through numerous complicated and time-consuming steps to reach this one critical moment in time. After the wax burnout and before the bronze pouring, the sculpture no longer exists as an object and is defined only by its absence in the casting mold.
While the casting molds are being heated in the kiln, the forced air gas fired furnace is lit. A silicon carbide graphite crucible, inside the furnace is charged with bronze ingots. The composition of bronze used at Studio Foundry is 95% copper, 4% silicon and 1% manganese. It is called Everdure Silicon Bronze. In order to know what quantity of metal is required for this pouring, a wax weight to metal weight formula is used. The ratio for bronze is approximately ten pounds for every one pound of wax.
As the bronze ingots in the furnace begin to melt, more ingots are added, charging the crucible until the desired amount is achieved. Fluxing agents, which enhance the pour and trap impurities, are added toward the end of the melt. The metal is then watched closely as it reaches the appropriate temperature for pouring, which for Everdure bronze is between 1940 and 2050 degrees Fahrenheit. The desired pouring temperature is estimated for each mold based on various characteristics unique to each sculpture to be poured. When the bronze reaches the required temperature, the ceramic shells are removed from the hot kiln and carefully placed on a bed of sand, stabilized with the pouring cups straight up.
The crucible is removed from the furnace with lift out tongs. The glowing crucible, charged with molten bronze, is placed in a pouring shank.
Any slag or impurities that have floated to the metal's surface are then removed with a skimmer. A two-person team lifts the shank, containing the full crucible, and carries it to the awaiting molds. The pour yard becomes quiet as the crucible is tilted toward the open cup, and a steady stream of iridescent-gold liquid flows from crucible to mold.
Once again, as with something akin to magic, the sculpture exists as a solid object.
After the pour is complete, the molds are allowed to cool. The cooled casting, encased in its ceramic shell investment, is then devastated. Much of this work is done with air tools, switching to hand chisels as the sculpture's more delicate areas are revealed.
SCULPTING IN BRONZE
The spruing system with gates and vents, once in wax, is now in bronze and must be completely removed. The surface of the sculpture is chased and retextured to match the original. Many works are cast in sections and must be welded back together. When the metal chasing is complete, with utmost attention paid to every detail with regard to the design and surface quality of the original, a final sandblasting is performed, removing all oils and contaminates, preparing the bronze surface areas uniformly for patination.
THE PATINEUR'S PALLET
Patination is the process of applying a patina. Metal coloring, (patining) is not an exact science, but depends on the technical skill and artistic judgment of the patinuer, working closely with the sculptor. Patinas are used to create life-likeness in sculpture, and are used symbolically in both abstract and representational contexts, and more generally to unify and enhance the aesthetics of a work of art. Although patinas may be thought of as a secondary characteristic of sculpture, often applied in a process that is distinct from that of creating the art work, in many cases it is the key factor in the visual coherence and artistic significance of a piece. Therefore, a patina is of prime importance.
The long term relationship between the sculptor and the patina specialists at Studio Foundry contributes greatly to achieve the distinct quality represented in the often multicolored bronze sculpture created for the artist. Both hot and cold patina applications are used. Bronze reacts with certain acids and other chemicals by oxidizing in different colors. For example, cupric nitrate applied to a hot bronze will oxidize with the metal changing its color to green. Studio Foundry, well known for its innovative patinas, has developed a broad pallet of colors exclusively for our clients. The patination process also enhances the ability of the sculpture to sustain the effects of time and the elements.
(The sculptures illustrated in this description are original works of art by Ron Wicks, Kevin Erben, Michael Hall and Rosemary Malone-Hall ).