mould making

Plaster Room 03/12/18

Weekly Summaries, Work in Progress

Today I got the third and final rose ran up, then attached to the cup with the rest using hot knives and wax. Then I painted a layer of shellac over everything, to help the grog to stick to it, and once it was dry I covered it all in first coat grog.

Once that had set we put the plastic cylinder over it all, and I layered scrim (netted fabric) and plaster along the bottom, to seal the cylinder to the board, and around the middle of the cylinder for stability. As soon as this was set I spent the rest of the afternoon mixing and pouring second coat grog, to fill the entire cylinder to make the mould ready for the kiln.

Really proud of my progress today! Got loads done, and worked hard to get the mould ready for the kiln. It doesn’t look like I’ll have a chance to pour before the break, but at least when I get back it will be all ready to go.

Prepping the Moulds for the Kiln/Setting up for the Pour

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Before the moulds could be fired in the kiln, Becky removed the plastic from the outside (that we had used to make the moulds, as seen in previous posts, and the brick video). We then had to cover the sides and bottom of each mould with layers of scrim coated in plaster, to create a protective barrier to stop the plaster moulds falling apart in the kiln- four of us did this, and I didn’t take any photos as it was very messy! But you can see the moulds with their plaster coating in the above photos. The moulds then went into the kiln upside down, as you can see in the photos. They go in upside down so that as the mould is heated and the wax inside melts it will flow out of the mould, leaving empty spaces where the metal will then be poured.
The next step was to vacuum the insides of the moulds to ensure they were free of debris, ready for the pour. Once this had been done the moulds were ready to be winched into place using the pulley system in the foundry, and set up in the sandpit ready for the pour.

The video shows the technicians winching one of the moulds into place, I kept out of the way for this part as I hadn’t done it before and wanted to watch and make sure I knew how to do it for the next moulds. I then had to dig the moulds in, making sure the sand was packed in closely around each mould to ensure stability for the pour. To keep the moulds clear each one had a piece of wood placed over the top.

This was definitely one of the more arduous parts of the process- it took five of us to do the plaster coating, and four of us to get the moulds from the kiln into the sandpit, as each one was incredibly heavy and fragile. I was careful to follow all instructions from the technicians to make sure nothing went wrong!

 

Putting the Waxes into Moulds

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These photos show the process of prepping my wax bones for the kiln.
Process:

  • I started by pressing the waxes into clay, separated by a layer of cling film to make it easier to remove the clay at a later stage. I built up the clay a little to help hold the waxes in place
  • I then joined the waxes to create runners (where the metal would flow through) and risers (where the metal rises out of) using wax tubes, straws, and sausages of soft wax, depending on the thickness of each bone. I added additional runners made of soft wax to any points on the bone that were smaller, thinner, or looked like they would benefit from it and joined them onto thicker parts of the bones or onto the main runners
  • Once I was happy with how the runners and risers and I had degreased them with meths (to help the grog stick) I then began to layer up the first coat grog mix (2:1 grog and herculite) starting off with a paintbrush to work it into the details of the bones. As the mixture thickened I then pressed it on and built it up around the waxes, making sure not to cover the main runners and risers (the pieces you can see sticking out)
  • When the grog had been built up enough and left to dry I then flipped them over, removing the clay and cling film, so that I could repeat the process of layering up the first coat grog
  • I then needed to extend the runners and risers further, bringing the risers at the bottom up to the top, layering with more grog as I went along, for support
  • As I did this Becky built up a base with grog, which we then used to stand up the separate parts of the mould, building the grog round the sides until it was stable
  • Next we had to get the cup onto the runners, using hot knives to join them and soft wax for additional support
  • Because of the heat we had to degrease and add more grog around the runners for support as we went, as we left one over night only to find that the wax had curved over in the heat
  • I then extended the runners using hot knives to join the pieces of wax tube, and bring them up to the top of the cup, again degreasing and layering grog as I went for support
  • The next stage was to fit a sheet of plastic around the whole thing, which we secured with duct tape, before mixing a batch of normal fine casting plaster. We then dipped some scrim into the plaster and used this to secure the plastic to the base- working extra plaster in to waterproof the join. We also tied some plaster dipped scrim around the middle of each mould to help stabilise it ready for the 2nd coat grog to go in
  • This isn’t shown in the photos but we then filled the mould gradually with 2nd coat grog (1:1:1 grog, ludo and plaster then 2:1 ludo and plaster) until it was to the top of the cup and left it to set

We made 3 moulds this way with the wax bones inside, but I will be uploading a more in-depth video showing the process of the two wax brick moulds once I have finished editing it!

Hot Rubber Moulds

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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.