LENHAM POTTERY MODELS
making high-fired semi-porcelain models since 1969
Seven steps to the Shire Horse Model: Step Three

This is
Step Three:
Intermediate
Mould-making

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Back to
Step One:
armature

 

Step Two:
modelling

 

Step Four:
making the
rubber model

 

Step Five:
plaster production
mouldmaking

 

Step Six:
slip casting

 

Step Seven:
fettling and finishing

 

Back to the
Introduction

Making the intermediate mould, Page One of Four.

Beginning the intermediate mould making on the finished plastilene model.

It is not possible to make a production mould against the plastilene model. The modelling compound is too soft as well as oil-bound. The oil would be picked up by the surface of the plaster mould and prevent the plaster from sucking the water out of the casting slip. An intermediate positive model has to be made from permanent material. The first process is to cover the plastilene model with a two-part RTV silicone rubber mix. Many coats of the catalysed rubber are painted on, waiting for the material to cure after each coat. The tail has had only one coat, and the modelling material can still be seen.

The short cylinder under the tail matches the bit sticking out on the horse. These make holes through which the resulting moulds will be filled.
It is essential that the silicone rubber is carefully weighed out and the catalyst weighed or measured with scientific accuracy. This shows the balance which we made here. The brass arm balances on a knife edge at the top of the pillar, and the pointer is accurate to 1 gramme. I have outlined the brass pointer otherwise it does not show up in the photograph. I collect a lot of plastic tubs, many of the same size and weight, because the used one is thrown away after mixing. The weights were the only items purchased. From left, 50 gr, 20 gr, 10 gr, all metal. On the right, plastic and metal 5 gr. The 1 gr. weights are large ball bearings.

The next page shows the finished rubber mould.