Casting Glossary of Terms

Casting Glossary of Terms

Bands and Straps – are used for securing multi-piece molds for slip-casting.

Bisque – refers to ware that has been fired once and has no chemically bonded water left in the clay and does not have ceramic glaze. Sometimes also known as biscuit.

Bisque Firing – is in the low-fire range. It drives off the water and carbon from the clay and fuses the clay particles together. From this stage, water can no longer be added to the clay and reform the object, it now has a set shape. The resulting piece is hard, but it is also porous and able to absorb a small amount of water from the glaze solution.

Bone Dry – The condition of clay when all the water has evaporated. The clay is completely dry.

Casting – Forming pottery by pouring slip into a porous mold, usually made from plaster.

Casting Slip – A fluid clay (slip) of high specific gravity, obtained by deflocculation and used for forming ware using the casting process. Casting tables – are designed to hold casts while in the process of working. They are long tables with wooden bars evenly spaced along the top to hold large and small casts. The casts are laid on the table and using a slip gun they are filled up with slip through the pour hole.

Clay – A combination of fine grain mineral fragments. The result of decomposition of rock possessing the properties of plasticity, porosity, and vitrifiability.

Cleaning Greenware – the process of removing mold seam lines and imperfections from unfired clay objects.

Deflocculation – The dispersion of clay slip by the addition of an alkaline electrolyte e.g. sodium silicate. Fettling – to trim or clean the rough edges

Fettling – to trim or clean the rough edges of (a metal casting or a piece of pottery) before firing.

Greenware – Unfired clay ware. Flashing – is a think line of slip that forms along the seam lines.

Gravity – Specific gravity is defined as the comparison of a liquid’s weight with the weight of an equal volume of water.

Greenware – A ceramic piece that has been completed and dry but not yet fired.

Hard Spots – Areas that will reject color, and sometimes cause ware to have bare spots. Commonly caused by improper greenware casting.

Kiln – Pottery oven or furnace in which ceramic products are fired. May be fired by wood, coal, sawdust, electricity or gas.

Kiln Wash – A mixture applied to the top survey of kiln shelves to protect them against glaze drips and runs.

Leather Hard – Partially dried clay ware. The ideal stage for turning fettling, sponging etc. The clay has lost its plasticity but looks moist.

Model – the original or prototype of the piece to be made. Usually in clay and occasionally in plaster.

Mold or mould – a hollowed-out block that is filled with slip, ceramic raw material. The liquid hardens or sets inside the mold, adopting its shape. A mold is the counterpart to a cast.

Plasticity – A workable property of clay that enables it to take and hold any impression.

Pouring – The process of filling a plaster mold with casting slip (liquid clay) to create a clay object.

Pour Gate – the opening in the mold where the slip is poured.

Turning – is the process of finishing the greenware (unfired ware) after it has dried to leather hardness. The technique is used to smooth and finish foot-rings on wheel-thrown wares or undercut places on molded or jiggered pieces.

Seam – A ridge formed in greenware where mold pieces join.

Slip – The suspension of a clay body in water, for casting ware in molds. Deflocculates are added to keep the clay in suspension.

Spare – That is the clay shell that formed in the pour gate. This is usually done with a plastic fettle knife.