Technical Details of materials.

The material I use for slip-casting is the result of 30 years experimenting although based on published recipes. The greatest proportion is white earthenware clay, sold in solid de-aired blocks. This is a commercial product which I think of as plastic clay, because I also incorporate additional china clay, quartz and feldspar in powder form. This way, I have reduced the plasticity of the clay but increased the whiteness and heat-tolerance of the material which could now be regarded as semi-porcelain. The powder and plastic clay are mixed together with water and deflocculant into a runny liquid which will fall through an 80’s mesh sieve held in a vibrating oscillator.

It weighs in at about 34 to 35 ounces by weight to one pint by volume. If you wish for an accurate recipe, please send SAE OR ask for it by e-mail.

When the models are dry, I spray the colour on the horses. The addition of too much water will cause the clay to weaken, so it has to be done carefully and allowed to dry before firing. However, spraying colour onto a dry surface enables me to make a horse into a piebald (white and black)or dapple by brushing off unwanted splatter. Then horses, models or dolls house 'china' is sprayed with clear or white gloss glaze and fired.

I say it is 'high-fired' because the usual range for earthenware clay is 1080 deg. C to 1100 deg C. With this recipe I can fire to 1140 deg. C, which results in a harder and less absorbent material. I put the word 'china' in quotes, because I don't want a purist to complain that bone china is fired over 1280 deg. C, which makes is translucent. True porcelain is fired to a hot yellow heat, 1350deg.C upwards, and becomes vitrified.

Next column for Methods.
Forward to Mould-Making.

Technical Details of Methods.

This home-made liquid slip is poured into plaster-of-paris moulds. Dry plaster sucks the free water out of the adjacent surface of the liquid clay. The unwanted and still liquid slip is poured out of the mould, which is allowed to dry for an hour or so resulting in a cast which can be handled, with care, when the mould parts are eased off the stiffened clay.

I call them ‘multi-part moulds’ because many potteries use plaster moulds, but I have never seen more than three or perhaps four parts used by a commercial concern. They make their working moulds in dense plaster or perhaps silicone rubber ‘case’ moulds because they need the repeatability and interchangeability of parts that comes from identical moulds. Figurines may be cast in several sections, for instance, legs, arms, heads, and reassembled while stiff enough to handle.

I designed my horse and dog models to be cast as one whole body including the legs and head. The only part cast separately was the tail moulding, which is frequently used to conceal the filling and emptying hole. This means that a typical mould for a standing horse model will have nine to ten parts, plus two for the tail. I have found that this is the better procedure. It means a longer and more complicated job mould-making but easier assembly. I also feel the structure of a large horse is stronger because there are no weak joints.

The same method of multi-part moulds is used for the Dolls House China, particularly the baths, where the feet are cast in place. Some of the more simple shapes are one-part moulds (basins) or two-part moulds (jugs).

Fettling is the removal of the lines which are left by the separate mould parts. I make tap holes, etc. in the clay when soft, fettle the horses when leather-hard, and finish off the items with sponge and water when nearly dry.

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