< LOST PATTERNS
SUITABLE MATERIALS FOR LOST PATTERNS
As we have seen, the artist’s original sculpture or MASTER PATTERN, is always used directly in the investment mould when creating a lost pattern cast. This means that the artist is restricted to modelling their design in only those materials which can easily be flushed from the investment mould during the kiln burnout.
Traditionally, artists working with the lost pattern technique have used wax as their modelling material of choice. As well as satisfying all the technical demands of the casting process, wax is also an excellent modelling material in it’s own right. As we will see in later sections, wax can easily be blended to create a variable working medium; BLENDS can be formulated to make either a very hard, or very pliable medium - or a perferred balance between these two extremes. Wax can also be COLOURED to suit personal preferences. Few wax blends deteriorate or dry out in the manner of clay and related modelling materials, so with care, good quality wax sculptures can be kept in excellent condition for many decades. Hardly surprising then, that many artists use wax a working material, even when creating sculptures not destined for the foundry.
One practical difficulty when modelling in wax, is it’s tendency to slump – especially when working in warmer ambient temperatures. Small hand scale designs can be stored in a fridge (though remember, refrigeration can make wax temporarily brittle), anything of scale in wax should probably be modelled over a supporting refractory core (see previous page). If a small wax pattern is likely to slump, it is usually acceptable to model a design over a light gauge wire armature. A light armature made of soft solder may melt and fall out of the investment mould along with evacuated wax during the kiln burnout process. If a heavy gauge wire is used as an armature, copper wire for use with copper alloy casting metals, or else stainless steel is recommended, as both these metal can usually be safely left within a solid cast.
Of course many materials other than wax are also suitable for use with lost pattern casting, especially if a CERAMIC SHELL investment is being used for the refractory mould. The thin, but thermally efficient ceramic shell enables kiln heat to penetrate more easily into the mould and purge the contained pattern materials. In addition to wax, suitable lost pattern materials can include tallow and other fats, vegetable and organic matter including balsa wood, paper, card, straw, expanded polystyrene foams and fabrics to name a few possibilities. Even certain plastics and low melting point metals and alloys (lead, tin, bismuth, pewter etc) can be use for making lost patterns.
LOST PATTERNS – A SUMMARY
Lost pattern casting is a relatively quick, easy and cost effective method of producing small scale casts of models formed in low melting point materials. The founder does not have to produce a rubber reproduction mould, or a wax copy for casting, so costs are typically around 20% lower than a similar cast produced using a reproduction mould (dependent upon the complexity of the design and moulding materials normally used).
The artist is restricted in the materials they can use to make a lost pattern – they must be easily combustible and there are also usually practical limits to the scale of work that can be made. If any part of the founding process goes wrong, the artist may be faced with having to re-work the design from scratch. Not every founder is willing to take on lost pattern work, and those that do may not refund deposit payments in the event of a miscast. The founder may also surcharge the artist if the cast is excessively heavy, or if the cast requires a good deal of extra finishing due to faults arising from a poorly prepared wax.
Most lost pattern casts are intended as ‘one off’ or unique casts, though an edition can be produced by 'lifting' a rubber mould off the completed metal cast at some future point.
PERMANENT PATTERNS >
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