I have had a lot of experience in working with plaster as I used it as a primary material for making work on my BA in Fine Art. I have also made a number of moulds since I started my own ceramics studio practice. These have included, two part press moulds, slump moulds, hump moulds and I have also made sprig moulds and slip casting moulds. Below are some images of moulds I have made and used since starting on the MA. I am planning to make some more large scale hemisphere slump moulds to enable me to create larger curved forms in the future.
I am always on the look for items that can be used as the ‘pattern’ for the mould, anything from ping pong balls to exercise balls, rice containers, old crockery items etc. I use mould makers soap as a release agent and utilise offcuts of lino, stiff plastic or containers with their bases removed to act as a cottle (wall) to retain the plaster. I ensure all seems and joins are sealed with thin layer of soft clay as plaster can seep through the tinies of gaps and escape. I ensure that the ratio of plaster to water is sufficient, I usually use the ‘island’ method of sprinkling plaster into water, but have also used weight and volume ratios too. When pouring I endeavour to minimise air bubbles as much as possible and for complex shapes I use a paint brush to ease the plaster gently into delicate areas.