Bronze Casting - Metal and Sculpture

Here is an explanation of some of the processes associated with casting bronze sculpture. Various types of bronze are discussed, together with the intricacies of the Lost Wax process.

In Part 1, bronze metal composition and history is discussed. This is the first stage in how to cast bronze.
Part 2, on the next page, describes the lost wax process.

Part 1 Part 2

What is Bronze?

Bronze is a copper alloy, a mixture of copper and other metals. Copper on its own is a soft metal. However many, many years ago someone discovered that by adding a small amount of tin, the combination of the two created a harder metal - and so bronze was born.

For centuries bronze meant copper and tin, often 90% copper with 10% tin. Over time other combinations have developed. Adding zinc to copper gave an even harder metal, usually referred to as brass. Also, a combination of lead, tin and zinc was added to copper; this is sometimes referred to as 'gunmetal' bronze and has been the traditional standard for much of the statuary bronze, often in a common combination of 85% copper, 5% tin, 5% zinc and 5% lead.

However more recently metallurgists found that adding silicon to copper created an alloy that poured and welded easily. Although silicon is not a metal, this combination, often 95% copper, 4% silicon and 1% mangan- ese, is referred to as Silicon Bronze. It is now popular in many foundries where the ease of casting and welding is much appreciated. However it is difficult to work with after casting because of its hard nature, and it is also less porous which makes applying the patina more difficult. Therefore, for many a bronze foundry, the traditional bronze alloy is still regarded as the best for casting bronze sculpture.

Creating a Bronze Sculpture

We will now try, in as simple a way as possible, to explain some of the intricacies of the 'lost wax' process. There are many variations within the process, but the process follows strict progression throughout.

The Sculpture
We must always start with the artist's creation. Normally the artist will work in either clay or wax, depending on the size and nature of the piece they are creating. For a small piece this may be all he needs, otherwise they must first create an armature: a structure using metal, wood and other material onto which the artist can apply the clay or wax. Using simple tools, an artist can create sculpture limited only by their skill and imagination; but now we must turn it into metal.

...continued in Part 2