During the last rotation of my workshops i had to opportunity to try slip casting. In the past i have never connected with clay/ plaster based project so i was a little bit apprehensive to begin with.
I decided to cast one of my favourite mugs, a glass mason jar styled vessel.
The first step was the build up clay to the half way mark of the cup. Seeing as i was making a four part mould i ensure that i left the top open as a pouring hole and filled in the bottom. if the base was left open the plaster would not come away from the object due to its con-caved shape, it would be trapped.
I then worked with the clay until it was as smooth as possible. This is done so that the mould fits perfectly together and will in future keep the slip from seeping out.
I then surrounded the clay and mug with board to create a boarder for the plaster . I measure 2 pints of plaster powder and mixed it with water to double cream thickness .This was then poured into the mould and set within in 20 minutes.
Once that was set using a 2p coin i engraved notches. (a whole in the plaster). This will fill up when the next layer is poured on top allowing the pieces when dry to easily fit perfectly together.
Before i added the plaster i had to wipe the previous side of plaster with soft soap. This is an industrial soap that creates a boarder within the top layer of plaster. Stopping the slab from absorbing the liquid of the next layer that about to be poured. This is done 3 time due to the porous nature of plaster. This step also allows the pieces to to be taken apart once the mould is finished.
These steps of building plaster slabs was repeated 4 times until the vessel was surrounded. The mould then had to be dried for a couple a days with the cup inside. This allowed the mould to stay in shape and dry out so no liquid would be absorbed.
Once that was done i was able to take the object out and fit the mould back together with elastic bands securing it. I then poured in slip with is a mixture of clay water and another chemical. This was poured into the mould and allowed to partially set for 20 minutes. I then poured the exess slip out leaving a dried layer coating he inside of the mould. I then allowed to dry upside down for one hour allowing it to fully dry. At this point i removed the mould leaving me with a fairly soft clay cup. I was then able to manipulate or add decoration like other clay features. The next step is the bisque fire the slip cast and glaze.
I found the process a little bit tiresome, seeing as it involves a lot of timing and waiting. But considering i dont usually like clay i enjoyed the process more than i thought i would. Im very glad i learnt this skill as i imagine it will be useful.