Bubble problem solved with fat busting machine?

Part of my development of the new bronze casting is to find a suitable inner former to support the woven wax during its casting, so the inner core has to be able to withstand the heat of molten bronze.

Looking back into my research into ancient Greek casting techniques shows that by the late Archaic period (ca. 500–480 B.C.), Sphyrelaton went out of use as a primary method when lost-wax casting became the major technique for producing bronze statuary. This was replaced with solid lost-wax casting using a solid core or clay.

I want to use this method but replace it with a material that doesn’t shrink quite as much as clay, and use casting powder to make a solid block which I can carve into to create my desired shape. This block of plaster will then support the woven wax.

After discussing this with other artists and the foundry one of my biggest obstacles could be air bubbles. When mixing plaster and water you unavoidably get air bubbles in the mix, this is fine for usual plaster uses, but not if the plaster is going to be kiln heated to 800°c. As you know when air is heated it expands, and if it is trapped in a hard substance it will try and find a way out, this could cause an explosion in the plaster.

Many artists and specialists suggested a vacuum chamber or an oscillating plate to either suck out the bubbles whilst the plaster is wet or to shake the bubbles out by vibration. Both these pieces of kit are a bit on the expensive side, so it was back to the drawing board.

I was thinking about this problem and how to overcome it, so to help I typed in ‘Vibrating’ into a search engine. Along side the many items that vibrate for 'other’ reasons, was an exercise machine. You set the vibrating plate to your chosen level and stand on it. Apparently the vibrations help to get rid of fat deposits in the body, and I thought “If this machine can vibrate the weight of a person, it should have no problem vibrating a large bowl of wet plaster”. After some more researching I found a second hand exercise machine only 20 minutes drive from my home listed for only £30, a few emails later I was on my way to collect it.

So can my bubble problem be solved with a fat busting machine or will it just vibrate the plaster out of my mixing bowl and all over the floor? I’m not sure, but the machine is now safely in my little van awaiting the first day back in the studio after the Christmas break to give it a try. I can’t wait.

Research into ancient casting techniques

Research taken from Metropolitan Museum of Modern Art

“The ancient Greeks and Romans had a long history of making statuary in bronze. Literally thousands of images of gods and heroes, victorious athletes, statesmen, and philosophers filled temples and sanctuaries, and stood in the public areas of major cities. Over the course of more than a thousand years, Greek and Roman artists created hundreds of statue types whose influence on large-scale statuary from western Europe (and beyond) continues to the present day.
The earliest large-scale Greek bronze statues had very simple forms dictated by their technique of manufacture, known as sphyrelaton (literally, "hammer-driven”), in which parts of the statue are made separately of hammered sheets of metal and attached one to another with rivets. Frequently, these metal sheets were embellished by hammering the bronze over wooden forms in order to produce reliefs, or by incising designs using a technique called tracing.

By the late Archaic period (ca. 500–480 B.C.), sphyrelaton went out of use as a primary method when lost-wax casting became the major technique for producing bronze statuary. The lost-wax casting of bronze is achieved in three different ways: solid lost-wax casting, hollow lost-wax casting by the direct process, and hollow lost-wax casting by the indirect process. The first method, which is also the earliest and simplest process, calls for a model fashioned in solid wax. This model is surrounded with clay and then heated in order to remove the wax and harden the clay. Next, the mold is inverted and molten metal poured into it. When the metal cools, the bronze-smith breaks open the clay model to reveal a solid bronze reproduction.

Since the physical properties of bronze do not allow large solid casting, the use of solid wax models limited the founder to casting very small figures. To deal with this problem, the ancient Greeks adopted the process of hollow lost-wax casting to make large, freestanding bronze statues. Typically, large-scale sculpture was cast in several pieces, such as the head, torso, arms, and legs. In the direct process of hollow wax casting, the sculptor first builds up a clay core of the approximate size and shape of the intended statue. With large statues, an armature normally made of iron rods is used to help stabilize this core. The clay core is then coated with wax, and vents are added to facilitate the flow of molten metal and allow gases to escape, which ensures a uniform casting. Next the model is completely covered in a coarse outer layer of clay and then heated to remove all the wax, thereby creating a hollow matrix. The mold is reheated for a second, longer, period of time in order to harden the clay and burn out any wax residue. Once this is accomplished, the bronze-smith pours the molten metal into the mold until the entire matrix has been filled. When the bronze has cooled sufficiently, the mold is broken open and the bronze is ready for the finishing process.“

(see this article in full at MetMuseum )

Sketches for new woven wax shapes, which to choose first?

Exploring internal and external spaces of woven wax cont...

After discussing this with the foundry, one method that I would like to propose using would be to cast blocks of plaster on a set of stainless steel legs (using stainless steel legs ensures that they can withstand the heat of the casting). The plaster can be carved into the chosen shape or form to become a former for the wax. I would be working the wax directly onto the surface of the plaster in various weaving styles, the legs in the plaster allows the plaster block to be retained in the air, thus preventing the weight of the plaster crushing the wax. Once the weaving is complete the entire weave, plaster former and legs would go through the lost wax casting technique. Once the molten bronze is poured and cooled the foundry would cut a small section of the weaving to remove the plaster and legs, then the section of woven bronze would be replaced and welded back into place. 

Removing problems of inflatables will open up many avenues for styles of cast work in a way that is non restrictive. This could lead into new fluid forms that are delicate, weaves would not have to be thick and they could have open areas. I can explore the internal space of a piece and expand into the exploration of negative and positive space. The possibilities are endless once the technical restrictions of an inflatable or cartable former are solved.

Watch this space for developments …..

The experiments with learning crochet have worked well, and I have now transferred the technique to my work with wax.

Using a crochet chain stitch is the first step, this chain is hand crocheted and then the chain wound around a polystyrene ball to form the first halve of a sphere.

Step two, the chain is stitched together with a swirl weave, in the same manor as my willow weaving.

Latest pictures from the foundry, my three thirds of the woven wax sculpture are now safely surrounded with plaster and heading to the kiln.
It’s scary to think that all that hard work is going to be melted, but the voids left behind will make the all important mould in which to pour the molten bronze.

Investment of the woven wax sculpture

The woven wax sculpture is now in the safe hands of the experts of Pangolin Editions down in Stroud, were they are working their magic turning the wax into bronze. I will be posting images as the process progresses, the first batch following this post are of the initial investment process were the wax is first sectioned with thin walls of metal. The metal walls will aid the sculpture being split down into sections just like breaking a Chocolate Orange! As the wax sculpture has been woven at full size and the weave is so intricate they will be using the vacuum chamber to draw the moulten bronze through the voids in the cast.

Once the metal walls are in place the wax is covered with a casting material to create the hard shell around the wax, this will go in the kiln and heat up to a high enough temperature that the wax will melt out of the cast.