Sculpting in oil-based clay for casting in bronze

The first step towards making a bronze sculpture is the concept and design. I start by choosing a subject and deciding what emotion, idea  or story I am trying to convey. Next I spend some time making small rough sketches to get a feeling of placement and movement.

Once I've selected the best of the sketches, I make a small sketch in clay over a very rudimentary armature of wire, this sketch is called a maquette. I find it very helpful to make this small mockup as is gives me a chance to start working on the weight and balance of the work - very key elements. Sometimes I leave the clay quite rough, other times I refine the work.

You can click on the image below to see more on this work:

clay sculpture work in progress of girl reading a book. “A Good Read” ©Lori Kiplinger Pandy

I keep my maquette nearby as I enlarge the sketch into the size that I want the finished bronze to be cast. Sometimes I make my own armatures using wire and plumbing pipes. Other times I will use commercially prepared armatures - often it can be a combination of both.

“State of Grace” sculpture work in progress clay maquette ©Lori Kiplinger Pandy

Here you can see my small maquette for "State of Grace" - the second in my series of ascending women. I have built up my larger armature and roughed in the main mass of the figure of the woman. Here I'm measuring for size and placement of the armature for the hair and the cloth. I have sketched over the photograph to give myself guidelines to work from.

“Ascension” ©Lori Kiplinger Pandy. Spiritual figure sculpture woman rising - clay work in progress.

When the sculpture is finished, it's tim to make the mold. In this photo you can see the support armature in "Ascension". The fabric has been sculpted to cascade onto the base and will support the bronze sculpture when cast. A sculpture like this will need to be cast in many pieces, so the mold-maker will decide how best to make the mold. "Ascension" was cut into 7 pieces during the mold making and each piece was molded with a sprue (spout) in place to pour the wax. 

Molds with ceramic shells - Lori Kiplinger Pandy

The mold is made of urethane or silicone rubber, built up over many layers. Since it's flexible, a hard outer shell of plaster is made to keep the shape of the mold. Keys are put into the mold and the shell to aid in proper placement and sealing of the units together.

Wax chasing “Ascension” ©Lori Kiplinger Pandy

Next, hot wax is poured into the mold, swirled around poured back out. Cooler wax is poured in and poured out. The wax needs to be a consistent, about 3/16" of an inch.

Wax chasing “Ascension” ©Lori Kiplinger Pandy
Wax chasing “Ascension” ©Lori Kiplinger Pandy

The wax pieces need to be 'chased' - have all the seams and imperfections fixed and the pieces reassembled back into a sculpture again. Then I give the chased wax to the spruing department where they will cut this sculpture again, attach wax tubes to aid in the flow of air and bronze.

Wax-sprue “Ascension” ©Lori Kiplinger Pandy

Once spruing is complete, a shell of plaster and silica needs to surround the wax. This can take up to two weeks as multiple coats of slurry and silica are built up. 

ceramic shell making “Ascension” ©Lori Kiplinger Pandy
slurry

Next the shells are heated in the furnace to melt the wax out - while the shells are still hot, molten bronze is poured into the shell and set aside to cool.

Bronze pouring “Ascension” ©Lori Kiplinger Pandy
Breaking off ceramic shell  “Ascension” ©Lori Kiplinger Pandy

Once cooled, the ceramic shells are smashed off and the metal sandblasted to remove all debris.


Metal chasing “Ascension” ©Lori Kiplinger Pandy

When the sculpture is finally welded together and chased, the piece goes to patina. Here the metal is cleaned and treated with various chemicals and heat, waxed and lacquered to produce the lasting finish.

Hot patina bronze “Ascension” ©Lori Kiplinger Pandy

Finally, the finished sculpture is mounted onto a granite base. Each step, from pouring the wax to mounting the sculpture to the base is repeated for each and every bronze in a  process that takes from 8 to 12 weeks per sculpture.

Ascension D
Sculpture and all images. Unauthorized use prohibited © Lori Kiplinger Pandy 2000-2016
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