Types of clay:
is fired to stoneware temperature,1260º - 1300º. The high firing temperature results in a pure white and almost completely vitrified ceramic body (able to hold water without leaking.) However, it is always advisable to glaze any surface which comes into contact with food or drink.
I use grogged clay, which contains small ground particles of pre-fired clay, to give the clay body strength and help reduce shrinkage during drying and firing. It is fired to 1260ºc. This clay also contains a certain amount of iron: this, together with the high firing temperature, results in darker tones when using coloured slips and underglaze.
A finer clay body, which is fired at the lower temperature of 1030º centigrade. Mainly used for how bright colours remain after firing. This clay should always be glazed as it remains porous and can get dirty with use.
has a lot of grog in it to help the pot withstand the thermal shock of the raku firing process. Naked raku is fired to under 1000ºC and glazed raku is fired to 1020º. The firing process for raku is very exciting and full of the risk of the pot cracking. The glazed piece is put into a small gas-fired kiln, brought up to temperature rapidly - 40 minutes or so, as opposed to about 18 hours for an equivalent earthenware firing. Once the temperature is reach and the glaze is evenly melted, the kiln is switched off and the pot removed immediately to be placed on the ground, covered with combustable material (paper, sawdust) and covered to smother the flames. Smoke is created, which the porous clay body will absorb. The glaze crazes and carbon is driven into the tiny fissures.The pot cools for a while, then is cleaned up and you see what you get!
Naked raku uses the glaze, with a sacrificial base of slip beneath it, as a shell. The piece is fired in the same way as glazed raku. After the smoking process the pot is removed from the ashes and water is poured over it. The glaze shell pops off, the layer of sacrificial slip washed off and a pattern of soft, smokey lines and dots is revealed. The piece is cleaned thoroughly, dried and then given a layer of wax to bring out the colour and protect the surface
All raku pieces are for decorative use only. They are too porous to hold water.
is liquid clay which has powdered stains mixed in. This can then be painted onto the still-damp pot to give an overall body colour. Very useful for naked raku.
is used for adding colour to small areas of the pot, such as painting in detail. When fired to stoneware temperatures it can form a semi-glaze surface, which I use a lot for ornamental pieces.
comes in many forms - clear, dry, crystalline, matt, glossy - the list goes on. This is where the alchemy of ceramics really comes in. The colours and textures come from mixing certain ingredients in precise measures to suit the clay body and the firing temperature.
are small pieces of clay pressed into clay or plaster moulds. They are then attached to the clay body with a dab of the liquid clay being used.