The mould will be made out of plaster, so in order to comfortably remove it from the head when it is finished, I need to make it in two halves.
I put a dividing clay wall on the top, and support the back with plaster and scrim (no bandage still) using clingfilm (ceran wrap) first to keep the other half of the sculpt nice and clean. I use thin strips of clay which bend easily over shapes, and then just wipe a small tool over the clay to get a nice smooth surface.



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Because I want to make the mould in two halves, I make keys or 'joggles' in the clay using the handle of a screwdriver. These will then help the two sides join in the correct position The screwdriver handle gives me a smooth, rounded indentation which will be reproduced in the plaster. I prefer these to 'hard edge' shaped keys, which can chip easily. There are tools for this (many made by mouldmakers themselves), but the result is the same.


And voila-the wall is ready and waxed with a little spray wax. Lets get busy with the first layer of plaster.
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This plaster (Crystacal R) has a good working time of about 15 minutes, so I mix up a batch (known as a 'gauge' of plaster), and then add plaster to water to get another gauge ready, but I don't mix it yet. I brush on a layer with the first mix (pic. 1), and keep slapping it on all over until I have a nice layer all over the sculpt and up to the edge of the clay wall (pic. 2).
Occasionally I wipe a plastic scraper or kidney over the edge to keep the edge clean-this is known as 'striking off' or striking the edge.
Pic.3 shows the jute scrim going on. I pre-soaked this so it does not rob any moisture from the plaster, and apply about four layers all over, smoothing down each with the second mix of plaster. I add the second mix before the first has had a chance to set, ensuring bestter adhesion as fresh plaster doesn't stick well to a dried plaster surface.
Pic 4. The finished half, with clean edges and chunky sides to accommodate clamps later, and reduce any distortion or warping of the mould. Not that likely on a mould this size and shape and not really that much of an issue if it did, but old habits die hard

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First up, I carefully peel off the supporting plaster behind the clay, taking the plastic film with it.

The clay peels away from the plaster surface easily. Hurrah. This is fun, like peeling sunburn-I never tire of this.

The cleaned up mould half, now ready for the other side. A quick squirt of wax to guarantee an easy parting later, and we are ready for the next side.

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The second side is much the same-a first layer followed by a second with scrim. I decide to cover the tiny undercut caused by the eyelid with a little clay (arrowed), just to be safe. Plaster won't flex at all, so any undercuts will cause breaks somewhere, and I don't need that!

Below is the finished mould. I will leave this overnight, and then hopefully pop it open tomorrow when the plaster has hardened up nicely.

You can just about make out the line diving the two halves, and the edges are nice and chunky, as they should be. Thin walls and edges will chip and crack during the demould process, which will involve big screwdrivers etc to lever it open. The plaster surface is only about 20mm thick, so it should dry out relatively quickly. The scrim layers will help to ensure the mould is good and strong. I have a good feeling about this but we'll see in the morning if this is misplaced faith.
Happy sticking
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Stuart
©Stuart Bray 2009