The process used for fine art sculpture in bronze is known traditionally, and most frequently, as "lost wax". It is an ancient process dating back to early Egypt, and the techniques used today are largely based on the original principles. "Lost wax" means literally that the form to be cast in bronze is made in wax and, after the mould for the casting has been created over the original sculpture, the wax is burned out, leaving the cavity into which the molten bronze can be poured. Of course there is a lot more to it than that!
Before any sculpting can begin, the composition for the piece has to be created. A little north of where we live is Wenderholm, a beautiful coastal park which has a magnificent grove of mature Pohutukawa trees. The first step was to go there and get some appropriate shots to use. From these I selected the tree that would be the basis of the composition.

Taking the characteristics of form and texture, I then sketched the composition the sculpture was to be modelled on.

Once I was happy with the composition, the drawing was scaled up in the computer to the finished size of four feet across and the corresponding depth of approximately two feet.
The scaled drawing was then traced onto the prepared working surface.

As the sculpture for the Pohutukawa was to be a "one off", it had to be sculpted in materials that could be easily "lost" by burning. The most convenient material to use of course was wax, as it can be formed and modelled in various ways. Importantly though, the sculpture had to be kept as finely made as feasible so that the finished bronze wasn't going to wind up too heavy to hang on the wall.
To this end, it was going to have to be sculpted with a hollow back while meeting a minimum thickness.
Wax by itself wasn't going to be strong enough to support the structure so, a suitable method had to be devised to systematically construct the piece and have it hold its form as well. To solve the problem, I hit upon the idea of creating a malleable medium which I called "wax maché". This involved dipping pieces of corrugated cardboard into hot wax, then laying the soaked and coated pieces over a layered wooden foundation which more or less followed the contours of the hollow back.
The wax plugs seen in the foreground and along the branch section would eventually become solid bronze plugs, to be drilled and tapped for the rods that mount the piece to the wall.

Through several stages of building up, carving back and building up again, the work began to take shape.

From time to time the wax was carefully flipped onto its back to check for things like structural integrity and consistency of thickness, and to seal up any gaps. Some of the wooden portions of the construction actually remained as part of what was to be cast. By consulting with the foundry, I was able to ascertain that these pieces would be burned out of the mould cleanly along with the wax.

Eventually the wax work was complete and ready to take to the foundry. At this point it was taken over by foundry staff who, through their expert care and application, took it from a wax form to a fully finished bronze.
The Pohutukawa sculpture had been carefully fashioned in two manageable sections. Branch-like solid wax rods in various thicknesses, known as sprues, were attached to strategic points of both sections. Once the wax was burnt from the mould, these sprues would provide the tunnels through which the bronze could flow as it was poured in.

The sections were then ready for the mould-making and were dipped first of all into a fine slurry. This hardened onto the wax like an egg shell, recording every nuance of detail. From there the two moulds were built up through a series of increasingly coarser layers and set to fully dry out, before being placed in a kiln for burning out the wax.

Next came the most dramatic and spectacular stage of the whole process: the pour. With the moulds set in sand boxes, expert hands controlled the flow of the 1300 degree molten bronze through the maze of cavities transforming all the work to date into a durable piece of fine art.
Once the bronze had cooled and hardened, the sections could be broken out of their moulds and the metal work begun. With the sprues cut off, the sections were fixed together using bronze welding rods, and the sculpture was ready for finishing. This stage, known as fettling, involved any detailed metal work the bronze required, such as recreating the original surface texture where the weld was done.
Finally the colouration, or patina, was applied to the sculpture. Here the bronze was evenly heated with a torch and chemicals sprayed onto the bronze surface causing a reaction that gave the work the desired colour. The patina was sealed with an overall coating of a clear industrial wax and buffed to give the piece its classic sheen.
Complete, the newly created bronze was ready for display.