PROCESSES – BONE CHINA.
Bone china is made from a combination of 50% animal bone, 25% china clay and 25% china stone, this combination results in a very hard, pure white medium, which when held up to the light is translucent. A very beautiful material to work with, but considerable skill is required to successfully bring it to the finished state.
- The resin master is cut up into several pieces, depending on the complexity of the original design. Generally 3 of the 4 legs will be removed, along with the head, tail and possibly the mane and ears if forwards. Plaster moulds are made of each separate piece; these individual moulds can be made up of 2 to 5 pieces in themselves.
- When the plaster mould has completely dried, it is ready to start the casting process. Liquid bone china slip is poured into each mould and left to dry for a set time. The water from the slip is absorbed into the plaster mould and leaves a ceramic skin inside the mould. When this is at the desired thickness, the excess slip is poured out, leaving a hollow cast. When the clay is sufficiently hard, it can be carefully removed for the mould. All of the hollow parts are then stored in a damp box until ready for assembly.
- Assembly – each cast piece has the mould seams still in it, and these have to be removed by hand (using precision dental tools) and some detail may need to be added. All the parts are then joined together using a thicker piece of bone china slip known as ‘stick up’.
- Once the horse is whole again, it will need propping, as bone china is unable to support is own weight. Where the props touch the horse, aluminium powder is applied, as this stops the props from sticking to the horse.
- Biscuit firing – Once the horse and props have thoroughly dried out, they are ready to be fired in the kiln. The temperature is slowly increased to 1225 degrees, and will be held at this temperature for 1 hour and 20 minutes. At this point, the bone china vitrifies and shrinks by 12%, enhancing the detail on the finished horse.
- The seams that were removed before firing tend to return after firing. These need to be removed. This can be done with a high-speed dremel or by hand-fettling with diamond needle files.
- Glazing – gloss or silk finish. Once the seams have been completely removed, the horse is now ready to be glazed. The glaze is applied by hand with an air gun and, when ready, the horse is returned to the kiln to be fired again, this time at the lower temperature of 1090 degrees.