mold_making - Preparing plaster of Paris for mould making...

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Preparing plaster of Paris for mould making Materials : A 10-pound sack of plaster of Paris A large wash basin A large metal soup spoon Note : The proper mixing of plaster of Paris is of the utmost importance. It is the essence of successful mould making. If the plaster is improperly made, the plaster may harden too rapidly, may flake, or may form air bubbles on its surface. Follow the procedure below exactly and carefully. Procedure : Fill the wash basin about half full of water and set on a level surface. With the hand, lift out powdered plaster of Paris from the sack or container. With a gentle sprinkling motion, sifting the powder between the fingers, permit the powder to fall evenly all over the surface of the water. With the thumb rubbing across the fingers break up any lumps of powder, and let the particles fall between the fingers. Add powder in this fashion until the water is completely filled. Add more powder until it just appears in a dry state above the surface of the water, indicating that the water is fully saturated with powder. Do not disturb the water, nor stir the powder in the water during this sifting process. Permit the powder to remain undisturbed in the water for 2 minutes. Now with the spoon, stir the mixture very thoroughly but slowly from the bottom up and around, to release any air bubbles which may have formed in the water. Stir evenly but not too quickly, until the mixture begins to thicken. The plaster is ready to be used. It now may be poured or spooned around the model. See the next two parts of this lesson on applying plaster of Paris. After all the required plaster has been used, the plaster remaining in the wash basin should be washed out into a large container. This container should be emptied on the ground outside; never in the drain. It will quickly stop up the drain pipes. If the plaster hardens in the wash basin, it may be broken away and the scrap pieces thrown away. They cannot be used again.
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Making a two-piece mould Materials : Same as lesson VII, plus: 1 flexible steel palette knife 4 pieces of Plexiglas or other plastic nonporous sheet, 1/8 inch or 1/4 inch thick (for size see note below) 5 pounds plastic clay, any colour, well wedged 1 heavy lead pencil 1 strong teaspoon 1 simple glazed model, hole in the base (see text below) Comments : This lesson indicates the principles to be observed in making a two-piece mould. These principles are applicable to the making of any multi-piece mould. Fig 30 We shall select a ceramic duck as a model, as being a simple item with which to begin. Any simple model may be used. The model selected should have a smooth glazed surface with a hole in the bottom. "In the trade," moulds comprising actually three pieces, in which two of the pieces contain the cavity, and a third or bottom piece contains the gate and forms the base of the casting, are often called two-piece moulds. The pieces of Plexiglas will be used to form a hollow box, in which the plaster mould will be formed. Measure the length,
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This note was uploaded on 12/01/2008 for the course ARTST 12 taught by Professor Budgett during the Spring '08 term at UCSB.

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mold_making - Preparing plaster of Paris for mould making...

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