Making the bed and boxing up.
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Choose a rectangular base (of plywood, plaster, anything hard and reasonably waterproof) which is at least 25 mm. larger than the banana all round and 40mm. longer at the stalk end. Roll out a slab of soft clay which will be deeper than half the thickness of the banana, say 25 mm. thick. The banana will be embedded in this slab, so we can call it the 'bed'. Lay the banana on this bed, and draw around it with a pointed tool. Scoop out the soft clay until the banana nestles into the bed up to the break lines. |
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Smooth the clay surface with a modelling tool. It pays to be neat and tidy at this stage because it saves much trouble later on. Make sure that the clay butts up tightly to the banana so that liquid plaster cannot seep through. |
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Experts call the retaining walls a 'cottle'. I prefer to use the word 'wall' for a rigid board and save 'cottle' for a flexible strip of plastic flooring. The walls must be capable of withstanding the outward presssure of the liquid plaster which may weigh several pounds. The system illustrated is adjustable for length and breadth. The angles are mild steel. There is sufficient room between steel and wood to insert the four wedges which hold the construction firm. If making a really large mould (see Shire mould-making) I would reinforce this system with luggage straps around the outsides. |
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This shows the cone of clay which increases the neck of the filling hole, and adds a reservoir for the liquid slip. This cone is rightly called the 'collar', and the slip inside the collar is called the 'head'. There should be sufficient head of slip above the filling hole so that the pressure of the head forces the slip into every crevice of the mould. The slip in the reservoir should not be allowed to fall below the neck of the collar. The slip will be reduced in volume when the water content of the slip inside the mould is sucked out by the dry plaster. Box up and seal all the joints with clay. The mark on the top wall is there as a guide, it is 25mm above the highest point of the banana model. The liquid plaster should come up to the mark, otherwise the mould will not be thick enough. |
The next page is pouring the plaster for the first part.