Making ready and pouring the second part.
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This shows the first part being boxed up ready for the second part to be poured. Don't forget to put back the clay collar, because it will probably have come off with the clay bed. The first mould part should be soaking wet. It is a good idea to submerge it in a bowl of water, at least until no further air bubbles rise out of it. The plaster must be covered with a parting agent, otherwise the new plaster will stick to the old. I use a wash of clay slip, which can be quite thick around the walls, but as thin as possible on the surfaces next to the model. Seal the edges and corners with clay so that no new plaster can leak out or sneak in between model and mould. |
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For the scond part of the banana mould, the volume of water and weight of plaster should be the same.
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The coating of slip (not more than 1mm thick) next to the walls gives somewhere to insert a knife edge to prise the parts apart. If gentle pressure does not work, try immersing the whole mould in a bowl of hot water. Remove the clay cone which is the collar. This provides a handy hole into which to insert the nozzle of a mastic gun. Fill the original empty plastic tube with hot water, and then squeeze the trigger. This forces hot water under pressure between the model and the mould. If the parting agent has been well applied evenly all over the mould, it should then split apart without damaging either the mould edges or the model. |
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Tidy up the outside of the mould while still damp. There are various wood rasps on the market which are ideal for filing off the corners. The outside corners can be bevelled to make the mould more comfortable to handle when putting on the rubber bands which hold it together. Be more cautious with the mating surfaces of the mould. A gentle rounding is all that is necessary, just enough to be able to slip a knife blade in when releasing the slip-cast piece from the mould. |
The next page is more information on deciding on the break-line, and making an enclosed void (an orange).