Fresh cast

Casting-slip is the clay which is used for slip-casting. It is a liquid suspension of clay particles and chemicals mixed with water. The casting slip is poured into a Plaster of Paris mould until full, and then left to cast for a period of time. During this time, the dry plaster mould absorbs the water from the clay, leaving a layer of clay particles against the face of the mould. This absorption of water by the mould also causes the level of casting slip at the head of the mould to drop. The mould may need to be topped up occasionally during the casting process.

Once the cast has reached the desired thickness, the liquid casting slip in the mould is poured out, leaving only the build up of clay particles against the mould face. (This process is similar to Easter egg making, but not quite the same!). After a time, as the clay dries, it draws away from the mould face and becomes firm enough to support itself and can be released from the mould. The mould is tipped gently upside down (as in the case of a one piece mould) to release the cast, or the mould is removed from the cast piece by piece to expose the form.

The cast piece is set aside and at an advanced stage of leather-hardness, is ready to be fettled and sponged down for decoration.

Pouring casting slip into the moulds	Gently removing cast from the mould	Fettled and sponged slip cast......

HISTORY OF SLIP CASTING

The first records of making pottery in moulds date back to the Hellenistic Greece and the Roman Empire. A simple, hollow bowl shaped mould was made out of clay, with a design impressed or incised into the sides. This was fired, and then the inside smeared with clay and smoothed on a rotating potters wheel. The form pulled away from the mould as it dried. A foot, handles and rim were added once the pot had been romoved from its crude mould. This process of smearing clay onto the mould was later replaced by pouring a runny mixture of clay and water into the mould to coat the inside. As civilization advanced, clay moulds were eventually replaced by plaster of paris moulds, and so the technique developed over time into the modern day version we now use.

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