< FLEXIBLE MOULDS
FLEXIBLE MOULDING MATERIALS
Before the common availability of modern elastic polymers and plastics, founders used a variety of naturally derived materials to create reproduction moulds. These materials included vegetable preparations such as ALGINATE and AGAR AGAR (both derived from seaweed), and more importantly gelatine, which is also known variously as GELATINE, COLLAGEN and ISINGLASS.
Gelatine is derived from animal matter, extracted from either pork skins or de-mineralised bone (a similar substance, isinglass is processed from fish bladders). Whilst gelatine is best known for it’s use in food preparation, sheets of gelatine dissolved in water to create a ‘sol’, can be used as a moulding compound. Up until quite recently (1960’s), dissolved gelatine sol would be poured into a prepared mould case surrounding a master pattern, then allowed to set. A limited number of waxes (about half a dozen or so) could be extracted from the mould before it deteriorated. Being prone to shrinkage and bacterial attack though, gelatine moulds were never considered suitable for long term storage; the creation of plaster master patterns (that could be stored and remoulded later), was essential for larger editions.
ALGINATE is associated with dental impression techniques, but may be used to make specialist art foundry moulds. Alginate is available as a pre-packed powder, which is dissolved in water just prior to use. This material is normally safe in contact with living tissue and it is often used for moulding body parts, though alginate is not ideal for producing waxes for casting as it can shrink rapdily and severely. In most cases plaster of Paris is immediately poured into an alginate impression to create a positive HARD COPY, it is this hard copy that is eventually moulded in a more suitable rubber or plastic compound for foundry use.
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