< ABOUT REPRODUCTION MOULDS
FLEXIBLE REPRODUCTION MOULDS
The origin of the modern foundry mould is generally attributed to the Greeks, possibly the Samian founders of the 6th century BC, but certainly 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 the ‘Historica Naturalis’ (xxxv) [ref].
The reproduction moulds of Lysistratos and others of this era would probably have been formed in a conveniently available medium, BLACK PITCH is the most likely. This substance would have been difficult to handle and a 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 impression materials, and employ a variety of mould construction techniques. Today’s materials and techniques that can easily accommodate the broad range of pattern sizes, forms and surface intricacies seen in the average art foundry.
Key to all flexible mouldmaking is the ability of the reproduction medium to closely follow a master pattern’s form, then permanently fix the image as a surface impression. Although the reproduction medium sets permanantly to the shape of the the master pattern, it has the ability to temporarily deform, then return to it’s fixed shape as before. Materials that are capable of this are said to have a quality known as ELASTIC MEMORY. Once set, the molecules that make up such elastic materials align in a manner 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, thus 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 infinite, limited only by the imagination of the artist, occasionally the laws of physics and finance of course! Some sculptures are composed of very simple forms, with little in the way of surface textures and detail. Many other sculptures are made up of far more complex and detailed elements, often accompanied by an extensive working of surfaces in the form of texture and contour.
Sculptors who model detailed textures and forms into a their designs can easily create overhangs and deep surface pockets in the work. These features are typically referred to as UNDERCUTS. Undercuts would normally 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 may be damaged and/or the mould rendered useless when the founder comes to disengage these two items. There are methods of accommodating undercuts when plaster piece, or sand moulding (both of which are rigid moulding media), but these adaptive techniques are time consuming, and do not always offer a satisfactory solution to the problem.
The advantage of using a flexible moulding material is that the 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 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.
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