< MATERIALS FOR PERMANENT PATTERNS
CLAY & FIRED CERAMICS
Clay plays a central role in sculpting, and this is no less the case when creating designs for metal casting. Many clay types have excellent handling characteristics which makes them an ideal choice for those artists who primarily work with modelling techniques. As well as being suitable for modelling, clays are generally economic to use (recyclable), and relatively simple to keep and handle in a studio environment.
Most artists use grades specifically prepared for modelling, such as ‘buff’ modelling clay, though other natural and processed clays (including proprietory trademarked non-drying and oven fired materials), are no less useable when preferred.
Fired clay objects, such as those formed in earthenware (terracotta and other porous materials), raku (clay with added fireclay grog), bone china (calcinated bone, stone and clays) and porcelain (plasticised china clay with feldspar and silica), may also be used as foundry patterns.
The main difficulty in using unfired clay as a pattern material, is the perrenial problem of keeping the work safe and intact during transportation and later processing in the foundry. Designs formed in any soft material will always be vulnerable in a foundry environment, even if carefully handled – so the use of an original clay model as a foundry pattern cannot be recommended under most circumstances. Firing a clay model may prevent the design from an uncontrolled drying out (though it may still crack in the kiln), and also remove the risk of accidentally smoothing off features; but fired ceramics are still relatively fragile and it is often impractical to fire many sculptural designs either due to their size, or because they are constructed over wood, metal and other armatures.
Some sculptors arrange for the founder to mould clay models in their studio space and it may even be possible to hire a temporary studio at the foundry when constructing a larger work if the facility is available. Neither solution is entirely satisfactory as studio attendance by professional foundry staff can involve considerable expense or it may be be less than ideal for an artist to produce an important work in unfamiliar surroundings, possibly at some distance from their usual working environment.
In short, although clay makes for a fine modelling medium, it also makes a very poor master pattern material. By far the best solution here involves a translation technique that enables the artist to utilise the best working qualities of clay, and then fix the finished artwork as a permanent hard copy, suitable for transportation and foundry processing. This sculpting technique is known as ‘waste moulding’.
WASTE MOULDING >
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