< ABOUT REPRODUCTION MOULDS
FLEXIBLE REPRODUCTION MOULDS
The origin of the modern foundry reproduction mould is generally attributed to the Greeks, most likely the Samian founders of the 6th century BC, but was certainly in use by the time of Lysistratos of Sikyon two hundred years later, whose skill and ability to produce a ‘likeness through moulding’ was noted by Pliny in his ‘Historica Naturalis’ (xxxv) [ref].
The reproduction moulds of Lysistratos and others of this era would have been formed in a conveniently available material, BLACK PITCH being the most likely. Black pitch would have been difficult to work with and successful mould construction would have been a challenging test of the moulder’s skills. By way of contrast, the modern foundry technician can select from a range of specialist impression materials, they can also use a variety of mould construction techniques according to the demands of the job. Today’s materials and techniques that can almost always accommodate the wide range of pattern types and surface intricacies used by modern artists.
The key to all flexible mouldmaking is the ability of a reproduction material to closely follow a master pattern’s forms and surfaces, then permanently fix that image as a usable impression. Modern reproduction materials set permanantly to the shape of the the master pattern they are moulded to, yet retain the ability to temporarily deform before returning to their fixed shape as before. Materials that are capable of these characteristics are referred to as having an ELASTIC MEMORY. Once set, the [long chain] molecules that make up these elastic materials align in a way that always inclines them to return to their originally fixed position. The amount these materials can deform and return without damage or permanent distortion depends upon their exact composition, therefore a range of moulding compounds is available to the founder to cover most situations.
WHY ELASTIC MEMORY IS IMPORTANT
The possibilities in sculpture for exploring scale, form, texture and so on are limited only by the imagination of the artist, (and occasionally the laws of physics or finance!). Some sculptures are composed of very simple forms with little in the way of surface textures and detail, other sculptures are composed of far more complex and detailed elements and can contain a great deal of surface texture.
Sculptors who model detailed textures and forms into a their designs can easily create overhangs and deep surface insets into a sculpture. These features are typically referred to as UNDERCUTS. Undercuts would prevent the clean removal of a rigid moulding material, a situation known as a LOCK IN. A mould/pattern lock-in must be avoided at all costs because the master pattern can easily be damaged and/or the surrounding reproduction mould rendered useless when the founder comes to disengage these two items. There are techniques available for accommodating undercuts when plaster piece, or sand moulding (both of which are rigid moulding media), but these adaptive procedures are time consuming and do not really offer a satisfactory solution to the problem.
The advantage of using a modern flexible moulding material with elastic memory is that the set moulding compound can temporarily deform as it is pulled away from most undercut features, allowing it’s release from the underlying pattern. The mould then returns to it’s fixed position, ready for re-use. Elasticity allows artists to create volumes, forms and surfaces with relatively little regard for technical issues like undercut features and enables founders to produce high quality reproduction moulds quickly and efficiently.
FLEXIBLE MOULDING MATERIALS >
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