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Filling a ceramic plaster mold with clay slip

Stacks of greenware ready for fettling, wet sponging, then firing


The making of a piece of ceramic begins with a plaster gypsum mold along with a slip casting clay. With the mold secured by strong elastic bands or straps, the mold slowly filled through the opening in the mold which is called the gate. (Refer to top picture)

Normally casting time of 20 to 25 minutes produces a clay wall with a thickness of 3/16 of an inch. During the casting of the mold, check the level of the slip in the mold and periodically addor top-off with more slip.

Larger pieces, such as floor vases, table lamp bases, etc. will require more time to form a thicker clay body. When the slip reaches the desired thickness (use a clock ortimer), empty the unused slip into a pail. This slip may be used again to fill another mold. Turn the mold upside down and allow the mold continue to drain. This procedure is known as the 'drain-casting' method of casting. Other methods of forming clay might be the pinch method, the coil method, wheel turning, jiggering, and pressing. The same methods are used for casting earthenware, stoneware, porcelain or red clay slips. The plaster in the production mold continues to draw the moisture naturally from the clay. After some time, usually 45 to 60 minutes later, the clay begins to pull away from the plaster wall of the mold. This releasing action occurs because the clay body now has less moisture in it than the wall of the plaster mold. At this point, the new casting known as'greenware' must be removed from the mold. Release the straps or remove the bands holding the mold pieces together. Gently pull on the wet clay body or tap using your open hand on the mold. After the greenware has dried, the mold parting lines known as 'fettles' are removed using a knife or sandpaper. After the fettles have been removed the piece is further wet sponged to smooth the fettles and the surface.

The 'cleaned' greenware is now ready to be fired in a kiln to around 2000 F. degrees. The newly fired piece of clay is known as 'bisque' or bisquetware. The bisque is now ready for glazing. A cost of glaze is applied to the bisque by bushing, dipping or pouring the liquid glaze over the entire peice. After the piece has been glazed, it is fired a second time to melt and mature the glaze. This fire is known as a 'glost' firing. Further decorating can enhance the ceramic by applying fired-on ceramic decals, or applying a coat of mother of pearl or a lustre, or decorating using fine 22K gold.

There are many, many uses for ceramic products in today's life style.

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