Moulding and pewter casting using silicone rubber

This photographic essay demonstrates how to create a 2 piece MoldMax 30 silicone block mould from an original bamboo handle, and then use the silicone mould to create a pewter casting. Some of the advantages of using a silicone mould rubber are:

1. Picks up exact detail of original model to fingerprint detail.
2. It has the best release properties of all mould rubbers.
3. Can handle fairly high temperatures (enough to cast low temperature melt metal alloys such as pewter, tin and lead).
4. Exhibits very good chemical resistance.

	The original bamboo handle used to make the mould
	Rolling out modelling clay to a desired uniform thickness
	The clay is trimmed and ready to pack around the original model. The clay is also used to seal up the ends of the Bamboo.
	Placing the clay around the model
	Creating a pouring funnel in the clay. This will be the pouring point for the molten pewter.
	Laying up of clay around the model is almost complete.
	Melamine retaining walls have been built around the model to hold the liquid silicone rubber Round key registration points have been carved into the clay to ensure the 2 silicone halves match up. The white cable creates “runners” to help the flow of pewter to areas that may otherwise land up with air bubble entrapments.
	Spraying the release agent, which was allowed to dry for 5 minutes before the rubber was poured.
	Liquid silicone being poured over the first half of the prepared model, this will be the first half of the silicone mould complete.
	The second half of the silicone block mould being poured. It is essential to use a release agent here to separate the 2 silicone halves later.
	One half of the Material One (M1) support shell or "mother mould" pre made and preparing to cast the second half of the M1 support shell around the 2 piece silicone mould.
	M1 with some black pigment added been poured to create the 2nd half of the support shell.
	The mould has been split, the original bamboo handle removed and the mould is being prepared for the pewter casting. The silicone mould is first dusted with graphite powder, which helps to improve the surface finish on the cast pewter, as well as giving the silicone mould some protection against the molten pewter.
	2.5kg lead free Pewter ingot, which costs around R170.00 per kg.
	The pewter with a melting temperature of 240 deg C is melted on gas burner.
	Pouring molten pewter into silicone mould
	The mould is opened after the pewter has solidified and the cast piece can be removed and allowed to cool. This picture was taken of our first casting and didn't come out too well. For the second casting the pewter was poured at a much lower temperature (just before solidifying) and the casting quality was greatly improved.