Foundry visit

Recently I visited my new (best!!) friend and head Patineur at a Foundry in Hampshire to see how the whole business worked. 

They offer two types of casting- sand or lost wax. Taken on a tour through the warehouse, each room has it's own character, yet all  are united by a thick layer of ubiquitous metal and plaster dust. 

The wax room is hot and steamy from the wax 'cauldron' in the corner and the burning of the alcohol lamps. 

The wax cauldron

It's here that the silicon moulds are made from original artist's forms (clay models etc), which are then lined with hot wax. The hot wax is worked into the mould with a paintbrush if fine details need to be picked up. These wax models are attached to wax cups/funnels and sprues. 

The wax used is quite different to the jeweller's carving wax i buy and retains a sort of elastic quality during its cooling period, much like chewing gum.

The investment room has quite a different character. All wax models are taken here to get coated in a ceramic shell that is what will eventually retain the molten metal when the wax melts out.

Wax models get dipped in a liquid, then a ceramic 'dust' or 'investment' repeatedly to build up their shells. The mix increases in coarseness in order to, first, pick up fine details, then to accrue sufficient strength to endure the high pressure and heat of the casting. At this stage, a core is inserted so that the casting will be hollow (a large solid bronze statue would be immovable and ludicrously expensive!) and pins attach the outer shell to the core.

Here the investment is dried, they are all stood on their wax cups.

These little ghostly figures are then taken to the kiln where the wax is melted out. Then they're inverted and packed into a sort of steel box, surrounded by sand and the molten bronze is poured in, via the cups. Once cool, the ceramic is cracked off.

Next..... the boring chasing. My lovely and long suffering friend began as a Chaser at the foundry. Encompassing a massive gamut of processes, Chasing can refer to the grinding, sandblasting, cleaning up, welding shut the pin-holes, polishing up of a piece as well as the traditional silversmithing 'chasing' I was previously aware of. This is a hand-tooling technique using punches and a mallet.

Finally, a bronze sculpture will (usually) be given a patina. Below are some colour samples on cast bronze blanks. The blanks are half smooth, half textured for comparison of finish.

The process of patination can only really be understood and developed through practice, it is notoriously unpredictable and difficult to master. The art of a patineur lies somewhere between a painter and an alchemist, skilfully balancing the constant movement of the flame and brush with consistent concentration, removing heat and applying more at exactly the right moment. Often patinas are the result of many, many layers of chemicals and also circumstantial effects such as atmosphere, humidity and metal temperature.

Insider tip: although there are infinite chemicals recommended for use in patination, my friend recommends that pretty much the whole rainbow can be achieved through only four: ferric nitrate, cupric nitrate, bismuth and Liver of Sulfur.