Sarah Richards

From conception to the final bronze sculpture - The lost wax casting process

Bronze sculpture – a fiery miracle

The bronze casting process never ceases to excite me! The transformation of my wax or clay sculpture into a beautiful bronze is a fiery miracle, so in this part of my website I would like to share with you this amazing process.

I myself do not cast my sculptures but send my wax or plasticine artwork to the foundry. The process, as you will see, is complex and requires skills with many different materials. I make the originals, and then finish the work on each cast sculpture with the patination (colour, using chemicals) and polish.

In addition, I hope to bring you, the buyer/viewer, closer to an understanding of the true value of a bronze, not only because the artist’s skills required must be studied, accumulated and practised, but because of the length and complexity of the bronze casting process itself and the skills required for this.

I cast my bronzes at the Goodwin Foundry and the Sculpture Casting Services. I am fortunate to have both these foundries down the road from where I live in the KwaZulu Natal Midlands, South Africa.

Contact Kim Goodwin for more information on his foundry.

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Cell: 0828561106

Contact Bruce Knight for more information about his foundry.

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Cell: 0834470814

The maquette:

A maquette is essentially a small study for a larger sculpture. When I have an opportunity to create a large sculpture I will use the creating of a maquette to learn more about my subject and the pose or structure that the final work will take.  This is then shown to the client who may have commissioned this large work so they may get a good idea of what the final work will look like. At this stage changes are easy to make as the armature (skeletal structure) from such a small sculpture (up to 40cm height) is flexible and therefore easily changed.  From this study I will 'scale-up' for the larger work, making the creation of the armature easier with something  accurate to measure from.

I usually work with a wax (microcrystalline wax, paraffin wax, dye) or plasticine (fine clay powder (ball clay), mixed into melted microcrystalline wax and some petroleum jelly), made myself. This is put onto a simple wire armature, and built up and modeled until I am happy and ready to send it to the foundry or work from when scaling up for a larger work.

I usually cast the maquette into bronze as it also make a wonderful sculpture.

Wax maquette

Bronze maquette

Bronze maquette

Life-size bronze

The armature:

The armature is the structural 'skeleton' of a sculpture. It needs to be strong enough to support the modelling materials and accurate as it is not easy to make changes to it at a later stage.

Welding isn't difficult. All that is required are a few learned skills, lots of protective wear, the right equipment (small welders are relatively inexpensive and easy to use) and patience, liberating the artist to make strong armatures of any size.

Finishing the armature:

The metal armature is covered in chicken wire. This will be the final support for the modelling materials. Tin snips, long-nosed pliers and silicon covered gloves are essential tools.

Starting the modelling:

When I work on a large scale I usually use Rhinolite (also known as cretestone) or plaster-of-Paris as an inexpensive, carvable support before I apply Plasticine. The Rhinolite material can be mixed to a thickness that can be modelled and it remains plastic for some time before it hardens. It is a dry powder which is mixed with water; it may be stained with oxides. It can be modelled and layered, eventually setting hard. Great for large sculpture work!

I cover strips of newspaper with mixed Rhinolite, and apply this to the chicken wire so that it locks onto it, forming a skin. When it is hardened I continue to work more Rhinolite onto this skin, building up layers and beginning to shape the sculpture, sometimes carving back if required.

When this form is dry I start working in the details with plasticine.

Overview of Process:

This series of images shows the making of a smaller sculpture from armature to final bronze:

Dividing up the sculpture for mould pieces:

Silicon Rubber:

Silicon rubber is mixed with a catalyst. It is then put on to the surface of the sculpture, making sure no air bubbles form. The rubber is used because it is flexible and will capture all details.

The cap:

Plaster -of-Paris is then mixed with water and put over the silicon. Sisal is mixed with the plaster for re-enforcement. The dividing wall is removed and preparations are made to begin the next piece.

Preparing the next section:

The walls are removed and new ones are carefully placed for the start of the next section.

Removing the mould:

Bronze casting:

Preparing the wax copies:

Gating:

The sculpture is gated, with runners and risers made of wax which are joined by heat to the hollow wax sculpture.(These will act as air vents in the bronze pouring stage).

Dipping:

The wax is hollow and will be filled with an investment mould held in place by pins. The outer sculpture will be covered in a ceramic shell, which consists of many layers of slurry and Shamot.

Loosing the wax:

This is now put in the kiln, and heated until  the wax pours out, leaving a hollow space.

Pouring the bronze:

The hot, hollow mould is balanced in sand and the pouring cup placed upwards. Molten bronze, heated in a furnace is now poured in.

Chipping off the shell:

When cooled, the outer shell is chipped off, and the inside investment is drilled out.

Cutting off the Runners and risers:

The runners and risers are cut off using an angle grinder and other tools, and the sculpture is sandblasted to remove any left over shell.

Patina:

Lastly the sculpture has a patina put onto it’s surface. This can be many things but usually consists of chemicals which change the colour of the bronze to a reddish-brown, black or green. The sculpture is sealed with wax polish.

Research:

For me it is essential that I find appropriate and good reference material for any new sculpture I undertake. This can be through photography, observation, making drawings and watching videos of the chosen subject. This is so I can absorb the ‘feeling' and essence of the nature of my subject before starting. I gather and explore.

The maquette:

A maquette is essentially a small study for a larger sculpture. When I have an opportunity to create a large sculpture I use the production of a maquette to learn more about my subject and to establish the pose or structure that the final work will take. This is then shown to the client who has commissioned the large work so they have a good idea of what the final work will look like. At this stage changes are easy to make as the armature (skeletal structure) from such a small sculpture (up to 40cm height) is flexible and therefore easily altered. From this study I will 'scale-up' for the larger work, making the creation of the large armature easier with an accurate base for measurements.

I usually work with a wax (microcrystalline wax, paraffin wax, dye) or plasticine which I make from fine clay powder (ball clay), mixed into melted microcrystalline wax and some petroleum jelly. This is applied to a simple wire armature, and built up and modelled until I am satisfied. I can then use it as a reference for scaling up into a larger work or send it to the foundry.

I frequently have the maquette cast into bronze as it also make a wonderful sculpture.