Plaster turning, mold making and slip casting

The first step of plaster turning is to prepare the chuck, instead of using regular pottery plaster you must use plaster called Prestia, this is a denser plaster which sets slower, this allows more air to escape resulting in less bubbles in your turned form. Where as for mold making, pottery plaster is used which is more absorbent.

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Here you can see I have used a plastic sheet to wrap around the chuck and secured it with clay and string to make sure there’s no spillage. After pouring the plaster, it must sit for a two or three days to set before it’s ready to turn.

When lathing it’s important to follow the safety instructions, keep the tool rest close to the plaster, stand comfortably with your feet firmly on the ground and your elbows tucked in keeping strong grip on the gauges with one hand on top of the metal part and another holding the wooden handle. The main gouges I used were a rounded tool and a square tool, unlike wood turning the plaster is much easier to turn and there is no need to sharpen the tool as often.

These were the three main shapes I turned, I found the process quite easy but I needed to be careful I wouldn’t turn too much. I really enjoyed this process, I am much more confident plaster turning than I am wood turning. Having the technicians around to help to help advise me was a big help, this allows me to learn much safer and quicker.

The first form I turned was rounded, this meant that I had to do a three part mold, I really enjoy mold making but I struggle with finding the half way points. I had to re-create my first mold three times as I couldn’t get the plaster form out, I learnt a lot during this process about the importance of using soft soap. I wasted a lot of time during this process, I knew I had to improve my mold making but because of time limitations I decided to re-design the form to allow me to create a one part mold. While casting the rounded forms I also struggled to control the thickness as it varied through the form, this was also a reason why I decided to re-design my form to have straight edge. I did find creating a one piece mold much easier and quicker but it did come with it’s problems while slip casting as well, I didn’t create a plug for my cast so when I would pour the slip out, if it dried too quick it would often fall out the cast and collapse, I did resolve this problem by drying my cast on their sides but this made the walls a little uneven. I thought this would be a problem when trying to fit the lid on to the base of the tea pot, when I poured slip into the molds I waited around 30-45 minutes to thicken the walls of the tea pot so the lid would fit tighter.

 

I was very cautious at the start of this project to make sure the lid fit securely on to the tea pot, so it wouldn’t fall off when pouring. After I bisque fired the pieces they were still very secure but I hadn’t consider the thickness of the glaze, this is why some of my pots have very secure stiff lids. Next time I will definitely take this into consideration, this has made me want to experiment with different clay bodies as well, I think it’s quite nice for people to see the raw clay underneath the clay for them to see the source of the material.

Most of my market research focused on the handle designs. In my first design, I decided to replicate the form of the lid by adding circular slab pieces of clay on the sides for people to hold, this clearly would have problems while hot but it was a good start to find juxtaposition in the form. While constructing my forms together I really liked the form of the spout. While playing around with the idea and experimenting with how I could create one shape multipurpose, I decided to use the same cast to make the handle, this has worked great as the shape flows well through the form. The only problem I encountered was that it took a long time for the cast to dry whole.

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I think this process has been quite successful as it was my first time using these methods of making. There are clear design problems regarding functionality, the cup walls are too thick therefore next time I should wait less for the slip to set, and the lid is an issue because I had not considered the thickness of the glaze application. I think the form works really well, next time I will take into consideration all of the problems I have encountered.

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