We made a few plaster casts of the rocks which form part of a current work in progress of Hilary Jack’s, titled ‘Shadow of the Future’.
I then took a test work though to the rest of the stages towards a bronze. The rocks had left some dedbris in the silicone moulds so we cleaned these by brushing a thin layer of foundary wax and pealing this away again and the bits of rock with it.
Next we prepared the moulds to make the wax copies. We again brushed a thin layer of wax within the mould to make sure to catch all the surface details before joining the two halves together. This was followed by pouring in the wax and rotating the mould to make sure everything is covered and an even 3mm depth of surface captured.
Once cooled, the mother mould and silicone mould are removed. The wax copy is inspected for imperfections like air pockets caused by bubbles. The seam line and any of these are carefully tidied up (chasing) so a perfect wax copy copy of the origial object is achieved.
Then this is cut up!!
I had no idea quite how many skilled and lengthy stages were involved in making a bronze, so I was a little surprised when I had to carefully splice up my the wax copy I had lovingly laboured over.
But next came the spruing & gating which I really enjoyed. This involed joining (with a hot knife) the different sections of the wax copy to a tree of wax rods and a larger cup where the bronze would be poured. You are always having to think at least one or two stages ahead of yourself – the orientation and placement of each piece on the tree was really important as you had to consider the flow of the bronze and potential air blocks.
Once this was all joined we made a secondary mould/ceramic shell around the wax. This was done through a process of dipping the wax into a ceramic slurry followed by covering it with different grades of molochite (silica sand). This coats the wax copy inside and out creating a one piece hollow mould. Each layer is dried before another dip and until the desired thickness of ceramic wall is achieved.