By Jan King
The pedantic puppeteer's guide to plaster and a bit of glass fibre
MATERIALS
There are now so many different materials on the market which can be used to make puppets, props or sets, that it’s difficult to know what to use for what?
Are you sitting comfortably?
There’s wood, clay, plasticine, plastiline, lots of different sorts of plaster of paris, glass fibre, carbon fibre, latex rubber, silicone rubber, foam rubber, foam latex, vinamold, polystyrene, two-part expanding polystyrene, formasert, (what’s that?),.... whoah, hold on there!!!!
And I’m sure lots of people out there use other intriguing materials which I’ve never heard of.
GLASS FIBRE
What shall we make?
A puppet head of some sort?
Out of what? Glass fibre?
Yeah, great, really tough stuff. Strong.
To make a glass fibre head, you first need to model your head in plasticine or clay, make a two piece plaster mould from the model, use a RELEASE AGENT!!!, put glass fibre into the two plaster halves, let it dry, release the glass fibre halves from the plaster and then join them together. Simple, huh!!! Well, yes and no.....
You try releasing glass fibre from a plaster mould if you haven’t used a RELEASE AGENT!!!
The MOULD, by the way, is what we are about to make in PLASTER OF PARIS. The CAST is what we take from the MOULD, in whatever material we have chosen, in this case GLASS FIBRE.
How do you start?
Model your head in plasticine or clay on a dowel rod attached to a plywood stand.
Photo 1. Modelled head in clay
(Click the picture for an enlarged view, then use your back arrow to return.)
The head shown in Photo 1 is really just a stylised shape, sculpted in clay, modeled with no UNDERCUTS. This means that when the glass fibre is released from the plaster mould there is nothing to lock the glass fibre to the plaster - the inside of a nose or mouth, an overhanging eyebrow, or a huge chin, for example.
Should you want to model a more complicated head, with loads of undercuts, or make several glass fibre heads from the same mould it is much easier, although more expensive and more time consuming, to make the mould from SILICONE RUBBER. Hopefully, details of this may be included with a future Guild Newsletter.
We make the mould in two pieces, so it is relatively easy to remove the original plasticine or clay that the head was modelled in.
So, how do we do it?
Set up your modelled head so that it is held really securely in a vice as in Photo 2.
Photo 2. Head in vice with clay walls and supports
To make a two-piece plaster mould we need to build up a wall of clay to separate the two plaster halves as shown in Photo 2.
Roll strips of clay and flatten them and build the wall around the half way line of the head. Put supports under the wall, as the plaster will weigh quite a lot, and you may see the clay wall slide down the head if you don’t use them. Build another wall as shown to stop the plaster dropping off the edge.
MIXING PLASTER OF PARIS.
Easy peasy, you may say, you just mix a bit of water with a bit of plaster of paris, let it dry, and Bob’s your uncle. Well, yes and no.....
To start with there are loads of different types of plaster.
When I started making puppet heads in the 60’s I bought tiny little bags of Dental Plaster from Boots the Chemists. They may still sell them, I don’t know.
I now buy plaster of paris in 25kg bags from my local Keyline supplier.
Different types of plaster and their specifications are listed in a booklet, Plaster Waste-Moulding, Casting and Life Casting, by Martin Sharpe, available from Alec Tiranti Ltd, 70 High Street, Theale, Reading, Berks. RG7 5AR. Phone 01189 302775. This is an excellent source of information.
Photo 3. Mixing plaster
I have always used CRYSTACAL R, which is good for detail work, and DENTSTONE which is good for strength for moulds for larger objects, such as bodies. Mixing plaster of paris properly will be dealt with in a separate leaflet, but in the specifications for the different types of plaster it tells you how much water to mix with how much plaster. Crystacal R, for instance, is mixed with 1 pint of water to 3 lb. 10oz. of plaster. This may seem like a large amount of plaster, but it is correct.
Put a pint of cold water in a plastic container, weigh out the above amount of plaster and sprinkle the plaster into the water. Let the water soak into the plaster for a couple of minutes and then mix the plaster with one hand, getting rid of all the lumps and bumps and any hard bits which may be in the plaster.
There, it’s mixed.
Now, take some of the plaster in your hand and drop it onto your model.
Make sure it goes into any nooks and crannies with a fine paintbrush.
As the plaster of paris in your mixing container starts to thicken, gradually build up a layer at least an inch thick, as shown in Photo 4.
Photo 4. Inch thick layer of plaster over head.
Leave to dry for at least an hour, and then turn the mould upside down and remove the clay wall, without harming the modelled head.
Build a second retaining wall as shown, and then brush vaseline onto the plaster, as shown in Photo 5. This is to stop the second half of the plaster mould from sticking to the first half. Mix the same amount of plaster as before, and repeat the process for the back of the head. Allow the mould to dry overnight and then prise the two halves apart with two or three small screwdrivers.
Photo 5. Back of head, second retaining wall and brushing vaseline onto plaster
Remove the clay from the mould and clean both halves with water under a tap. Allow both halves of the mould to dry thoroughly. To make sure glass fibre releases from plaster, I use wax recommended by the glass fibre manufacturer. A layer of wax is put onto the mould with a soft cloth and allowed to dry. This is then buffed to a sheen with a second cloth. This process is then repeated four or five times!!!
Then, when you have achieved the most magnificent shine imaginable, you brush a liberal coat of PVA over the mould, and allow to dry see Photo 6.
Photo 6. Two polished halves and putting on coat of PVA
THE HEAD
First to be applied is a GEL COAT, which will produce the smooth surface finish. Glass fibre systems mix a resin with a catalyst in given proportions. Directions for the system that I use tell me that the gel coat is mixed in the proportions 12-15 ml. of catalyst to 1000 grams of gel coat. So, if I want to mix, say, 100 grams of gel coat to coat the front of the head mould, I use 1.5 ml. of catalyst, at the most, for this amount. The company that I buy these products from supplies calibrated pipettes with the catalyst, so that accurate measurement is easy.
For weighing out the gel coat resin you will need an accurate electronic scale, which weighs in at least 5 gram increments. Use an old ice cream container to mix the glass fibre in. Put it on the scales and weigh out 100 grams of the gel coat resin. Add 1.5 ml. of the catalyst and mix it in thoroughly.
Use an inch wide brush to put the gel coat into the mould quite thickly. Repeat for the second half of the mould.
Allow both halves to set and the surface to go tacky, but then go straight on to the next stage, which is to put on one layer of glass fibre matting with ordinary resin. Don’t make the mistake I made by buying the surface mat which I thought would be very light for the head, because it has no strength. Buy Light Chopped Strand Mat (300gsm / l oz per sq.ft.). Cut it up into 1.5 by 2 inch squares.
Mix the resin and catalyst in the recommended proportions, (probably the same as for the gel coat), coat the gel coat with resin and stipple in the glass fibre matting, overlapping the edges. Only lay down one layer of matting.
Allow the resin to harden, but try to lift the half of the head out of the mould while it is still flexible, don’t leave it for hours, it seems to part company from the mould more easily when it is still young see Photo 7.
Photo 7. Two glass fibre halves released from mould
Clean the edges of the cast up with a Surform or file, mix a small amount of the gel coat, spread it on both surfaces and join the two halves together. Wait till this is dry and clean up the join with files and sandpaper.
Screw eyes for marionette heads can be screwed and glued into the glass fibre.
The head can be smoothed down with medium to fine sandpaper, and given a coat of white emulsion as an undercoat as in Photo 8.
Photo 8. Finished head
Tiranti’s also produce a Technical Booklet dealing with Glass Fibre, called The Polyester Resin Booklet and a Sculptors’ Catalogue of all their products, available from the address given.
