Guest Speaker at the Last Meeting

Speaker: Darren McNicholas, of Dalchem www.dalchem.com.au

Darren described the development of silicone polymers in the 1940s. He described a wide spectrum of uses, extending to fabric softeners for towels and antifoam in beer making, but primarily focused on silicone rubber RTV2 moulding compounds.

The silicone moulding rubber is marketed today as a two-part product (base compound and catalyst) to be mixed together. The products fall into two categories:

1. polycondensation cure: tin is used as a catalyst, goggles should be worn, and it is not food safe;

2. addition cure: platinum is used as a catalyst. Some of these are food-safe and skin-safe.

Cure time is usually 12-24 hours.

Examples of commercial applications were passed around.

Darren warned sculptors:

• to allow for 0.5% shrinkage with polycondensation RTV2’s;

• moulds need to be properly sealed (vegetable oils, vaseline, petroleum jelly or commercial release agents) as silicon sticks to itself strongly;

• Addition curing moulding rubbers will be inhibited if the silicone comes into contact with any sulphur containing compounds before or during curing.

An interesting demonstration was made in about 10 minutes of making a green silicon mould of a small skull, in two parts, with interlocking projections (keys). It was suggested large moulds would need support material such as a plaster or fibre-glass case. It was also mentioned that the addition of fibres to silicone would allow bonding of the silicone mould to a case. Eg: chopped strand fiberglass, Hessian etc.

Michael Meszaros commented on the wide range of materials that could be poured into silicon moulds, including polyurethane; plaster; gypsum; low melt alloys such as pewter, tin and lead.

Comment was made that the range of heat tolerance may be over 200 degC

Comment was also made that the life of a silicone mould may be prolonged considerably by washing with warm soapy water, and aerosol release agents.

Gillian provided examples of the range of instructional books available:

• The Alchemy of Sculpture by Tony Birkes

• Casting in Ciment Fondu by E Folkard

• The Polyester Resin Booklet – Alec Tiranti Ltd

• Plaster Waste Moulding Casting and Life Casting – Alec Tiranti Ltd

• The Encyclopaedia of Sculpting Techniques by J Plowman (Quarto Publishing 1995)

Report by Geoff Williams, evening organised by Gillian Govan