call us now

+44 (0)1428 605453

opening times

10am - 5 pm

Specialists in the Sale of 20th Century, Modern and Contemporary Sculpture

Lost Wax Bronze Casting

Sculpting Methods and Materials

Bronze Casting – The Lost Wax

Bronze sculptures a popular investments within the art world as they are difficult to damage and don’t lose value. A broad spectrum of artists use bronze as their chosen medium for working with, there are a variety of techniques and methods that you can use to sculpt in bronze but the most common is the lost wax method.

The lost wax method of casting is a popular method because it is one of the most simple to work with, it has been used throughout history as far back as c.3700 BCE, which makes the works produced then approximately 5700 years old. The process has an easy to follow 12 step working method and can be used to make some of the most intricate and elaborate designs.

The Process:-

An artist begins by making an original model of their design in traditionally wax or clay – but can use another material so long as it is oil based which keeps it soft.

A mould is made of the original model using two shell like moulds, one soft normally made of latex or silicone and one hard which is commonly plaster. It is common for larger works to be made using more than one mould. Or is a model consists of thin expanses from the body of the model these would be moulded separately. While producing the moulds a shim with keys is placed between the two parts to allow the two pieces to be put back together accurately.

Molten wax is poured into the mould and swished around to allow an even layer to set on the mould – normally the aim is for 3mm of wax to reside on the mould; every mould maker is different and will have found their own preferred quantities of wax to make their ideal cast. Excess wax is then poured away.

The wax copy is then removed from the mould. The mould may be used again to make duplicates.

Each copy in then “chased” – this is where a heated metal tool will be used to hide any imperfections and remove the line which shows where the two pieces have been moulded together. Any additional pieces that were moulded separately would be added at this point.

The wax copy is sprued with a treelike structure of wax that will eventually provide paths for the molten casting material to flow and for air to escape. The carefully planned spruing usually begins at the top with a wax "cup," which is attached by wax cylinders to various points on the wax copy. The spruing does not have to be hollow, as it will be melted out later in the process.

The sprued wax copy is then dipped into a “slurry” of silica and then into a sand-like stucco – the combination of these two materials is known as the ceramic shell mould. This process is repeated until ½ an inch of the ceramic shell mould coats the wax copy.

This is then fired in a kiln so the shell mould can harden. When the mould is fired it melts the branches of the spruing and these will now become vents/tunnels which the bronze travels down.

The mould will then be tested using water to find any weak points where leaks may occur. Any holes can be repaired or additional holes maybe drilled.

The shell is then heated once again in the kiln, once dry the bronze is melted in a crucible in a furnace; the molten bronze is roughly 1200 °C. Once liquid the bronze is poured into the shell, which must be heated because if it is not the temperature difference would shatter the shell. It is then set aside to cool.

The cast is now released, hammering away the shell and removing the sprues which will be used to make future casts.

The metal chasing process is now used, the same as with the wax cast previously, this removes any signs that the piece has been through the casting process. Imperfections or pits from air bubbles can be removed by filing the surface.

 

Finally you have a finished bronze cast of your original model.

Post your comment

The Sculpture Park