Whilst working on the burn out moulds that didn’t work I also decided to make a few batches of hot rubber moulds. The process is lengthier, but once the final plaster mould is fired in the kiln the waxes will melt out leaving hollow spaces for the molten metal to be poured into.
To start the rubber needs to be melted in the machine, by being fed into the top, and the press placed on top of it, using gravity to push it down to melt. It then drips out of the bottom into a bucket to be poured. Whilst it is melting I prepared the objects, by applying vegetable oil to each object for easier release from the moulds, then embedding them into clay, creating tunnels with the clay for objects that were going to be solid (although for the brick shown in the photos this was not necessary as I wanted it to be hollow and this required one side to pour in the wax). I then made a tube out of metal or plastic secured with duct tape, and pressed it into the clay bases around the objects. The tube then needed to be waterproofed with extra clay, ready for the melted rubber to be poured in. The next step was to pour the hot rubber into the moulds, and leave it to set. Once it was set I then made a basic plaster mix and poured this into the leftover space in the moulds of the bones (not the brick) to create a flat base for them to rest on.
When the plaster had set I then removed the metal/plastic tube and the clay from the moulds, and flipped them the right way up, using a craft knife as shown to make a few cuts into each mould, to allow me to remove the objects from the moulds. Once this was done they needed to be thoroughly washed to remove clay residue, and then secured with elastic bands or duct tape ready to pour the wax into.