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CREATING A CAST WAX PATTERN

Permanent patterns (designs for lost wax casting), constructed in materials like PLASTER and RESIN cannot be directly incorporated into INVESTMENT MOULDS. The founder instead uses a [rubber] reproduction mould to create a cast wax copy of the pattern. Wax is used to fill the ‘negative impression’ reproduction mould, solidifying into a positive image reproduction. In the art foundry a wax copy of an artist’s design is often referred to as a WAX PATTERN.

The wax pattern is a near exact copy of the artist’s design – near exact because however well made, some of the materials used in this process, like wax and rubber, are subject to a degree of shrinkage. As a result the wax pattern will always be slightly smaller than the master pattern on which it was based. This should not unduly concern the artist, because the difference in measurement between the wax and the master pattern is not usually discernable by eye.

There are a number of methods the founder can use to obtain wax patterns from reproduction moulds. The exact methods used are variable according to the individual preferences of each foundry workshop, and the particular challenges of the job in hand. One of the most common methods is known as slushing.

SLUSHING

Slushing reproduction moulds can be briefly summised as follows: The wax worker first paints a layer of wax into an open reproduction mould, care is taken to ensure all the surfaces are carfully covered, air bubbles are removed and high points (in the mould), are built up slightly more than flatter area (this allows for hot wax 'washing off' as it passes into the mould). The reproduction mould containing painted wax is reunited and held together with special clamps (DOGS) and/or heavy rubber bands. A suitable quantity of wax is heated and then allowed to cool, usually until a skin starts to form on the surface. The cooling wax is then carefully poured into the mould, which in turn is rotated and gently tapped to remove trapped air. The mould is then carefully emptied whilst still being rotated. This techniqe deposits an even layer of wax over the surface of the mould, creating a hollow wax copy of the mould's imprinted design. The thickness of wax varies according to the size of the design, however most art foundry waxes are in the region of 3 - 6mm (1/8 - 1/4") thick. This wax thickness eventually becomes the the thickness of cast metal, so getting this stage of the process right is very important.

The founder will usually extract the wax from the mould and 'chase' (work) seams and any other minor faults from the wax pattern. Once this initial process has been done, most artists will then inspect the wax and make any ajustments of their own.

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