Casting the Jawbone

Photographs, river project, Work in Progress

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Casting the jawbone raised a host of issues that I didn’t realise would be a problem, but hopefully it will work out in the end. Before we could make a hot rubber mould of the jawbone Becky (the technician) and I decided to make a plaster cast of the jaw, as we felt it would be too fragile to make a hot rubber mould from directly.

STEPS

  1. Before we could begin casting I had to fill in the holes in the jaw (where the rest of the teeth originally were) with soft wax, so that it would be easier to cast. I also used a little superglue to secure the two teeth- we were worried that they may have come out of the jaw when we de-moulded it, so this was a preventative measure.
  2. I then pressed the jaw carefully into some clay and built up clay walls around it, and then applied a few layers of vegetable oil to the jaw to help release it from the mould once the alginate had set
  3. I mixed up a small amount of quick set alginate which I poured into the clay mould and left to set
  4. Once this had set I carefully removed the clay and rinsed the jaw and alginate, before greasing it up with more oil, and building up clay walls around it
  5. Another batch of quick set alginate was then poured over this, and left to set
  6. The clay was then removed, and the two halves of the mould separated and the jaw carefully removed.
  7. After cleaning both halves of the mould I fit them together and secured them with elastic bands, and was then ready to pour fine casting plaster into it
  8. The first attempt didn’t work very well and only the thickest section of the jaw came out, so for the second attempt after pouring in the plaster I moved the mould around to encourage the plaster to flow through the whole mould
  9. Once I opened the mould up I realised one half had not worked out, and the other half, where all the detail was, was too thin- to fix this I cut up scrim and layered that and some more plaster on top of it until it was thicker and stronger
  10. I then de-moulded it and created a hot rubber mould from that plaster cast. Because the detail was lost on one side I decided to make a flat mould, rather than a round one that needed to be cut open, to save materials
  11. The final photo on the slideshow is of the original jaw, first failed plaster cast, second plaster cast, and de-moulded wax cast of the jaw- as you can see there are a lot of details that need to be worked back into the wax by hand, but I am confident that it is doable

Hot Rubber Moulds

river project, Work in Progress

 

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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.