Something about clay

I know some of you wonder whether I spend my free time digging up the back garden to get clay for my pottery. I guess it’s time to get the record straight and give you an insight into clay in general and more specifically the clay I tend to use.
Not quite as exciting as digging up my own clay, I actually order ready-made clay and have it delivered! Even better, if I’m not here when it arrives I leave a key and find it neatly arranged inside the entrance of my workshop when I get back.

‘Clay’ is short for ‘clay minerals’ which are formed over long periods of time by the weathering of rocks, and is often found around large lakes or marine basins. It is a deceptively simple material, cheap and abundant. It is soft, pliant, plastic and impressionable, without grain or direction. It can be modelled, pounded, flattened, rolled, pinched, coiled, pressed, thrown on the wheel, cast into moulds… you name it. It can be made into works of any size and unfired clay can be crumbled, mixed again with water, and made into something else.

Firing clay changes its chemical composition for good, and converts it into ceramic material. Fired clay may be white, creamy, red, orange, yellow, grey, brown, black, speckled, streaked, translucent, textured or smooth, porous or dense like hard stone.

There are three main types of clay – earthenware, stoneware and porcelain. The difference is in their firing temperature, the strength of the fired material, its colour, density, or translucence.
Earthenware is low fired (up to 1100 degrees centigrade) and can be quite porous.
Stoneware is high fired (1200-1300 degrees centigrade), is vitrified, and can be as dense as hard stone.
Porcelain is usually dazzling white and contains elements of glass in its composition, it is normally used thin, is high fired, and can be translucent.

As I have mentioned before, most ceramicists buy ready-made clays, packed as clay bodies – blends of natural clays ready to use and suitable for practically any specification, i.e colour, plasticity, texture, strength, firing range and many others.

I use stoneware clay bodies made in Europe. I prefer darker iron-bearing clays for use with my blue glaze – that’s how I obtain depth of colour; bright clays with less iron for my whites – that’s how I get a clearer colours.

Firing it up, Anagama style

This month I have been able to place some of my pieces in an Anagama kiln belonging to my friend and fellow potter Meir Moheban

The Anagama kiln (Japanese: 穴窯 meaning cave kiln) is an ancient type of pottery kiln brought to Japan from China via Korea in the 5th century. It is a single chamber kiln with a firing box at one end and a chimney at the other. It is fuelled with firewood and requires a continues supply round the clock. Depending on the length of the kiln it could take anything from 48 hrs to 12 days.
A natural ash glaze is formed from the interaction of flames, ash and the minerals in the clay. The placement in the kiln also affects the glaze, those closest to the firing box get the most ash and are often covered in it whilst those at the back are gently coated in it. It takes as many days for the kiln to cool down as it takes to fire. In this instance Meir’s kiln was fired up for 7 days, it is now cooling for 7days and the big opening celebration is on Feb 2nd 2013. If you are around, pls join us for the kiln opening.