Bridgit Smith Mould maker

Interview by Ken Clark.

KC: How do you make a mould?

BS: I have to be very careful when I receive the plasticine models because the surfaces damage very easily. If the character is to be clothed it doesn’t matter so much where the mould lines should fall but I take great care to make them as unobtrusive as possible, following the line of the jaw, under the hair line or through a frown. I mark where I want the mould lines to be with a felt tipped pen, following natural creases. No matter how good you make your mould you will always be left with a slight join line. Now with that in mind we may ask the designer to include a feature which will give us a line to work to. Co-operation is the key to good design work. Once this has been done I make each part of the mould separately, leaving it to dry thoroughly before proceeding to the next section. It can be a lengthy business.

I did not have any training before I came here, but, if you think about it where could you go to receive basic training in this field. Research has to be done on the job. You puzzle out what you need and then puzzle out how to do it. Each new mould will present its own, often new, problems to be solved. It is a continual process of learning. For example, let us take the figure of a worm. No simpler shape you might think! But it has caused us so many head-aches; you see a worm has its natural lines around its body, which prevents you from putting a line along its length. However, if you put it in its rings it poses problems when you come to fit the skeletal armatures; and you would have to find a secure means of slotting all those segments together. Then we found that rubber moulds were not giving good casts so we tried plaster. The tail could not be seen to have a join line because it had to flick up so the end had to be solid while still able to receive the mechanics. But, to coin a phrase, we got there in the end.

Most of my work is done for Cosgrove Hall, although I am a free-lancer. I have as much work as I can handle at present and that’s the way I like it. I make all the moulds for all the models, using dental plaster because it is hard and more resistant to heat and it gives me more casts than ordinary plaster of paris, pound for pound weight. It doesn’t shrink as much either. You have to be aware of the shrinkage factor with the materials you use and make allowance for it when making the plasticine master. The green mould material is silicone rubber. When a solid resin model is called for I have to make a flexible mould to enable it to be released when dry. But because rubber is flexible I hold it in a resin impregnated bandage forming a case – this holds it firm while casting.

Of course, the bigger the model the bigger the problems, not the least of which is the cost. The rubber alone costs in the region of £80 a tin. One of the nice things about using the resin bandage is it permits you to use the minimum amount of rubber. I make the mould first and then before I take it apart I make the resin cases, thereby guaranteeing an exact replica cast.

How are you able to centre the mechanics so precisely in the mould?

We fix a ‘key’ to the end of the mechanics which slots into its partner on the end of the mould. The foam rubber mix is whisked into readiness and painted in very quickly. You have to work fast because it sets within a few minutes, although it takes a further two days to ‘cure’. Plaster shrinks a little bit, resin about 5%, rubber doesn’t shrink at all. If you are making a resin mould and a resin cast you would have to make allowance for 10% shrinkage.

How did you enter this profession?

My brother makes the mechanics for the models and as the studio expanded it was realised there was a need for a mould maker. I made one or two for them, which were approved and accepted and from then on I gradually took over general responsibility, until it became a very nice little job.

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Printed in Animator Issue 17 (Autumn 1986)