Week 2 (Week Beginning 01/02/10)

Hot Casting

On the Monday of this week I got an induction into hot casting. I decided to use some of the shapes I had already cut out of plaster and smoothed off, unfortunately one of the shapes was slightly undercut so it was hard to get the shape pressed into the sand so I ended up using just a bit of shape to press into the sand. So if I decide to do any more sand casting (which I probably will) I need to remember that there shouldn't be any under cuts and also the finish is important too, Simon suggested using car lacquer so the plaster is smoother and wont absorb the water in the sand and will leave a neater imprint.
In the image above on the right are the things I used for hot casting, had to put a handle on one of the pieces of plaster so I could push it in and pull it out easily, the handle was just a piece of wood glued on with araldite.I used gloves when sieving the sand so if there were any bits of glass in the sand I would cut myself on them, the trowel i used to flatten the edges of the sand where I had pushed in my plaster models, the largest piece of wood and the knife were used to get the pieces out of the sand after it had been cast, there is a small stick for poking air holds around the mould and water because it was really hot in there.
Before I could start forming the moulds in the sand I had to sieve it out first so the sand was nice and "fluffy", this was so that when the plaster was pushed in the sand had space to compact together and so that when the glass gets poured in any air can escape so there aren't any bubbles in the glass. Simon had put water in the tray of sand that morning so it needed to be mixed up and sieved out, he shoveled the majority of the contents of the tray into a bin then set up two long pieces of wood across the tray to rest the slieve on. When I had sieved out enought sand Simon used a piece of wood to flatten out the surface of the sand ready to push my plaster pieces into the sand.
When I had pushed my pieces into the sand I used a trowel and my fingers to compress the sand a little to hold the edge together and so its won't crumble when I use the blow torch on it. Next I wiggles the model from side to side a little so I could get it out without ruining the mould or knocking the sand out of place. When doing multiple sand casts you need to remember to have a decent amount of space between each of the moulds. When all the mould were all set out they need to be sprayed with a mixture of distilled or deionized water and graphite, one of the mould I didn't spray to see how it would look with the sandy then poked holes around the edges of the piece but not to close to help any air escape preventing bubbles in the glass.


Because the sand was wet it needed to be dried out before I could get glass poured into my moulds, to dry them off I used a blow torch to for a few minuets, for the first couple of minuets there was a lot of steam coming out of the moulds, so I kept going until there was almost no steam. Then I sieved a small amount off copper oxide into a couple of the moulds to compare to the kiln cast pieces that had copper oxide in too.
Simon then took a gather from the furnace on a iron with a ball at the end of it, the smaller pieces only need one gather but the larger pieces needed two. When Simon had dripped an amount of glass into the mould he held the hot end of the iron over the glass heat up the top of the glass so that it would smooth out.
The glass was left for a while to cool, then with a knife Simon cut around the glass to make a little jacket he told me it was to keep the heat in the piece and it helped with the annealing process and to minimise the contact with the glass. The piece of glass were then but on to a board and carried to a kiln for them to anneal. After the glass had been taken to the kiln I needed to mix and fluff the sand up (while wearing gloves because of the steams) and then smooth out the surface to make it easier for the next person using the sand to move around and sieve out, when I had done this I places a plastic sheet over the tray to keep the moisture in the sand. It took about 24 hours for the kiln to get to a low enough temperature for me to be able to take them out, and after I had taken them out they were still quite hot, so I was unable to clean the pieces in water but I was able to use a wire brush to dust away some of the sand that got stuck to the glass. To the right is an image of the results of my sand casting attempt, the two larger ones that look darkest are the ones I had copper oxcide in, the rest are just clear glass and the one in the middle of the smalles pieces is the piece I cast without spraying any grafite into the sand. I really enjoyed the process and was happy with the result, I plan on making some more plaster models to make a range of shapes to test with sand casting.