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'Washingtonia' bas-reliefCompleted bas-relief installedProgression from concept to completion

'Lost Wax' Casting Process

Below are examples of two projects using the 'lost wax' process of bronze casting.

'Washingtonia' Bas-reliefs

The Brief
My commission for this project was to create bronze bas-reliefs which were to be installed at the three entrances to a home on Sydney Harbour.

At upper left is a portion of the photograph of sails that was to be my starting concept. The photograph of a tall ship's sails was taken by the project architect during Sydney's Bicentennial in 1988.

The bas-reliefs were to state the name of the property, 'Washingtonia', which is the species of the mature palm trees that grace the garden.


Communicating the Concept
In order to communicate the concept clearly to my client, I drew up the design and digitally superimposed it on an image of the sandstone column at one of the entrances. The resulting image is at the left.

The client liked the look and I commenced work.


Creating the Work
The first step in creating the bas-reliefs was to size the work accurately relative to the column. To do this I decided a suitable viewing height and then designed where the rebated area needed in the sandstone would work with the perpendicular joints of the stonework.

This consideration led me to alter the proportions of the bas-relief panel and I checked this new shape on site using a full scale pattern.

Having confirmed the dimensions, I commenced the artwork. I chose to use clay as I find it naturally produces beautiful, organic curves.

Paper fibre added to the clay enhanced the firmness of sharp edges where required and bulked the clay, helping it to resist shrinkage.

Once I had determined the size of the lettering, I had it laser cut in acrylic sheet and glued it to a backing board to maintain its position.

The clay forms were built around the lettering, the modelling process allowing me to experiment with mass, complexity and simplicity until I was happy with the piece.

The clients had seen images of the work in progress but, as always is the case with sculpture, the quality and strength of the forms has to be seen in order to be fully appreciated.

Once the finished artwork, (at left,) had been viewed by the clients it was time to take it to the foundry.


At the Foundry
Making the bronze casting
Here the clay artwork was moulded in synthetic rubber. This mould was backed up with a plaster mould to hold the soft rubber in shape. The mould was then opened and the original artwork removed.

The mould was closed and molten wax was then poured into the mould. The mould was opened again and the wax copy of the original clay artwork was removed.

This wax copy was then supplemented with wax rods which will create the pipes, (sprues,) that will supply the molten bronze evenly to all parts of the mould and other pipes, (risers,) that will create the pipes that will allow venting of fumes from the mould as the bronze is poured in.

This wax construction was then covered with many layers of powdered ceramic material and liquid binder to form a ceramic mould which carried the shape of the wax copy to the next stage. The ceramic mould was then fired in a kiln and the wax was burnt out, leaving an empty, vitrified ceramic mould, capable of handling the heat of the molten bronze.

This last process is why this method of casting is called 'lost wax'.

This mould was then inverted and molten bronze poured in.

When cooled, the ceramic mould was broken away to reveal the bronze casting. The bronze sprues and risers were cut off and the surfaces were hand ground and polished.

As we had three panels to make, we made three wax copies, each of which went through this entire process.

Patination
Patination is a colouring of the metal itself rather than an applied finish like paint or coloured polyurethane. As such, it is a live surface that will mature, deepening over time, and each panel will uniquely colour in response to its location.

The bronze was first heated evenly using a large blow torch. Care must be taken here so as not to overheat finer details and bronze thicknesses,

Liver solution was brushed vigorously, but evenly, onto the hot metal in the direction of the long lines of the forms, (see image at the upper left). This solution creates the very dark portions seen in the finished patina. When this part of the process is completed, the whole panel is a dull, dark grey.

A 3M pad dipped in clean water was used to gently rub back the liver from the areas that I wanted to highlight. Judicious removal of the liver renders a gradual change from dark to light across the surfaces.

The panel is then reheated to dry and a solution of Ferric Nitrate is applied sparingly by brush. By alternating the application of this solution and blow torching to increase the heat of the panel, the colouration that the ferric gradually changes the bronze from a golden honey colour to the rich red that that was wanted on these panels. This colour change is quite subtle under the dull, grey surface so it requires careful monitoring to know when to stop!

As the panel cools, the colour becomes more apparent, (see the detail image at the upper left).

A protective wax is brushed onto the still warm panel, whereupon it melts and bonds strongly with the receptive metal surface. The wax acts like clear oil on timber, in that it highlights depth and richness of colour, allowing the surface to mature over time whilst still protecting it from the elements.

I have used a microcrystalline wax that was developed for the British Museum bronze artworks. This wax has a high heat and UV resistance and is the most durable protective finish for bronze in our climate.



'Frond' Bas-reliefs

The Brief
When the 'Washingtonia ' panels were finished, the client requested me to create a bronze object to occupy the circular recesses in the seven sandstone columns that made the high retaining wall at the street boundary.

I chose to use the shape of the 'Washingtonia' frond as the basis for this object. I liked the idea of using the geometric elements of this organic object to hark back to the name of the property and still relate to the curved surfaces of the larger bronze panels that would be visually referenced with them.


Creating the Work
Having received approval from my clients for the design concept sketched in plastilene, (see image at left,) I then made a timber pattern using a domed, disc shape as the starting point, (see image at lower left).

By choosing to only cut and reorient the disc segments, I retained the simple strength and grace of the disc's surface. I then bound this interplay of curves and edges together with the encircling form.

This pattern was shown to my clients and then taken to the foundry where the same process as the panels produced the bronze objects, one of which can be seen at the lower left.

Bronze lugs in the back of each casting were drilled and tapped to allow me to screw stainless steel studs into the piece for mounting into the sandstone using epoxy.




~ Roger Apte SCULPTOR ~

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