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.
- 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.
- 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
- I mixed up a small amount of quick set alginate which I poured into the clay mould and left to set
- 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
- Another batch of quick set alginate was then poured over this, and left to set
- The clay was then removed, and the two halves of the mould separated and the jaw carefully removed.
- 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
- 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
- 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
- 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
- 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
Photos of the wax casting process- melting the wax in a saucepan before leaving it to cool to pouring temperature (the wax needs to be cool enough that it coats the side of the pan), then pouring into the secured moulds, including the larger brick mould, before de-moulding and removing excess wax/working the details back in.
Video of two wax casts, fresh from the mould- you can see that there is excess wax that needs to be removed, and some of the details need to be worked back in to the casts.
Video made up of a clip showing the second, larger batch, of wax casts fresh from the moulds, followed by a clip of me working on one of these casts to remove excess wax and work a hole back into the cast to mimic the original bone. The final photo is of the wax cast from the previous clip next to the original bone I cast it from- you can see that I have worked some of the details lost during the hot rubber mould process back into the wax cast.
The two clips in this video show the first hollow wax cast of the brick I found on the river, and the second cast next to the original brick- you can see how the hot rubber mould picked up most of the detail from the brick, and how that has translated to the wax casts. You might notice some lines on the casts- this is because to make a hollow cast you need to pour in the wax slowly and roll the mould gently around to ensure the wax coats the mould properly- I did this too slowly so there are lines visible. Next time I use the mould I will be careful to pour the wax faster to avoid this happening- I may melt these two casts down and redo them. The brick casts need to be hollow as to make a solid bronze of that size would be too costly, and too heavy. I will either have to leave the hole in the bottom, or weld a small piece of metal over the hole, but this is something I will tackle when I get to that stage.
Unfortunately this was all I was able to get done before the workshops closed for the break, but I am looking forward to getting back into the foundry/plaster room and continuing my work! The plan is to make at least two of each bone in wax, and then make at 2 – 4 large moulds to go into the kiln and then be poured, as I want a copy of each bone in aluminium and in bronze. I have also been shown a material called glass wax, which is used in the film industry to make objects that mimic glass, and if I can afford it I would like to experiment with this medium as well, as it will give me another material and colour to analyse.
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.
I couldn’t go into too much detail about the research on either project, but it is all below on my blog if you would like to see it- I preferred to focus on the practical work I have been doing, as a lot of work goes into it that you don’t necessarily see when you see the final pieces.
I haven’t updated in a while, as I have been busy physically making work in the foundry this term, which takes up a lot of my physical and mental energy- it is a very hands on, time consuming process, and at the time of writing this I have no finished pieces, as my first mould did not work.
The photos above show the process of making the mould.
- The bones were first pressed into clay, which then had plaster poured over the top of it. This photo shows the second stage, where the clay has been removed and cleaned away, to reveal the bones embedded into the plaster
- The next stage was to join each of the bones together with soft wax sausages, moulded by hand- this would later become the channels that the metal ran through
- The soft wax sausages then needed larger hard wax tubes attached, using hot knives heated over a Bunsen burner to melt and attach them- the top tubes would become channels for the hot metal to run through, and the bottom ones were for ventilation. The wax and bones then needed to be de-greased so that the grog (a special mix of plaster) would stick to it
- I then began layering on the grog, carefully over the wax and bones, so as not to damage or dislodge them, extending the wax tubes at the top of the mould as I did so
- This photo shows the additional wax tubes added as I applied grog- the joins on the wax tubes were wrapped with the soft wax to strengthen them
- Another stage in the grog process
- At this point the mould was stood upright, using more grog, onto the board I was working on, and the wax tubes further extended
- Once it was upright I then needed to build soft wax around a paper cup, to create the funnel for the top of the mold, which was then attached to the wax tubes. I added more grog as I went along for support, as the wax tubes were very fragile, and the cup was heavy from the added wax
- I then made a cylinder out of plastic using plastic sheeting and duct tape, to fit around the mould. To keep it in place I used fabric dipped in plaster to create a band around the middle of the mould, about halfway up (for support) and more of the fabric dipped in plaster around the bottom (to seal the plastic to the board)
- The next stage was to make the second coat grog mix (it is made with ludo instead of fine casting plaster) and carefully fill the cylinder to the top with this mix. This had to be done slowly, in stages, to prevent the heavy mixture from damaging the rest of the mould, and also to make sure it was completely filled.
- Once it was set Becky (the technician) removed the plastic layer, and covered the outside in fabric dipped in plaster to make a sturdy outer layer, and the mould was then fired in the kiln at a very high temperature to melt the wax and burn out the bone fragments. This photo shows the mould once it had been filled with molten bronze and left to set
The video above shows the pouring process in the foundry, done by Becky and another technician. My mould is the middle one!
12. This photo shows Becky removing the outer layer from my mould
13. We then began to smash my mould open (carefully) to see if it had worked
14. This photo shows the broken mould- you can see the metal has filled the cup and the top of the wax channels, but stops at the bones
15. The fragments of bone in my hand- this mould failed as the kiln did not get hot enough to burn the bones out, meaning the metal had nowhere to go.
I was very disappointed that this mould failed, but it was an experiment, and myself and Becky realised that the kiln was not going to be able to reach the kind of temperature we needed without it breaking my mould. This mould took me nearly two months to complete, as I had to wait between each step to check with Becky that I was doing it right, and to ask what the next stage was, as it was my first time doing this, but I am already halfway on the shell mould. This is because once you know what you are doing it is much easier to just get on and do it, which I will continue to do! Also I have only been in the foundry 3 days a week, as Wednesdays it shuts at 12.30 and I struggle to get in early enough, and Fridays it is shut. Going forwards I plan to finish the shell burn out mould (hopefully it will work) and also continue making wax versions of some of my bigger bones, to make into a mould. My next post will show the process of making a hot rubber mould, and waxes from that!