Mould making rotation 2

The mould-making rotation is next we will be doing plaster moulds for slip-casting and press-moulding. The final objects should follow a theme, mine will be mechanical abstract. To start decide how to cast the chosen object 2 or 3 piece mould? Then find the half-way line by measuring with a set square, some objects already have a useable half-way mark. Most of my objects are plastic so are made in moulds and have a mark. I start with a plastic margarita glass which has a half-way mark. I build up clay around it up to the half-way line also coming out approx 2-3 inches from each side into a rectangle. The straight edges are to make the boards easier to place. The boards are placed around the clay edge the sides and joins are sealed with soft clay. A brick is used to estimate how much plaster is needed; plaster is quantified in pints to kg. The plaster is made and then poured over object and clay. When the plaster is set the boards are removed, and the base of the plaster smoothed with a sander thing. The clay surrounding the object is removed except if there is a ‘bung’ for the spare slip. The ‘bung’ is moved to create a mirror of itself in the next piece of the mould. Flipped over with the object still in the plaster, notches are made with a 2p coin or I find a tea spoon easier. The plaster is then wiped over with soft soap to prevent the next layer of plaster sticking to the first. The boards are put up around the plaster and object, more plaster is poured on top to make the second piece of the mould. When the plaster is set the boards are again taken away the sides and top smoothed. The mould can then be opened and the object taken out. Rubber bands are put around the mould and it is left to dry out completely. The mould will be ready to pour slip into.