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The Craft of Pottery Making

The Craft of Pottery MakingPottery Making Introduction

Pottery is one of the most ancient of crafts and is unique in its blend of the four elements – earth, air, fire and water. The attraction of this alchemy and endless possibilities for the potter keeps the craft as alive and exciting today as it was thousands of years ago.

Origins of Pottery

Today’s studio potter throwing a bowl on an electric wheel can trace the origin of the technique back to the hand turned invention of Egypt in 3000 BC. Up until 500 BC, everywhere in the world, pottery was earthenware – low temperature ware that was still porous and named after the earth from which it was made. At the time the Chinese developed the skill of making stoneware which is a high fired, impervious pottery so named because of the stone like ring it makes when it is struck.

Clays

There are two main types of clay; earthenware and stoneware. Both are sold in various colours from white and cream to green and red (red earthenware clay is well known as terracotta). Some potters prefer to blend their own clay by adding in ingredients like iron oxide to create speckles, molochite (ground, fired clay) for strength, or stains to create artificial colours. At the coolest end of the earthenware range is Raku and at the hottest end of the stoneware scale is porcelain which becomes almost translucent when fired.  

Clay is supplied in damp solid form, well wrapped to prevent drying. Before anything is made the clay must be properly prepared and all the air bubbles removed. This process, called wedging, is not unlike kneading dough and needs to be done on an absorbent surface to prevent the clay from sticking. A slab of thick plaster or board covered in stretched hessian are suitable. Each potter finds the most comfortable style of wedging for themselves, but the process must be repeated until all the air bubbles have gone. The lump can be sliced with a cutting wire to check that no bubbles remain.  

Waste clay can be dampened down and this mixture (slurry) is then dried on a plaster block or bat and used after re-wedging.

Basic techniques of Pottery

Pinch pots – As the name implies these are made by pinching clay between the fingers. A ball of clay is cupped in the palm of the hand and the shape formed by squeezing the clay upwards and outwards between the thumb and the fingers on the other hand. No water is necessary but the result must be of an even thickness because a pot with a thick base and thin rim may crack when firing. The finished shape can be smoothed off with a damp sponge.  

Coil pots – Clay is rolled on a flat surface into sausages of an even thickness and coiled around a base of clay. One coil is pressed on top of the next and the pot built up to the desired size. Coils overlapping inwards will make a cone and outwards will produce a bowl shape. It is important that the coils are joined together well or they will break apart during the firing or drying. The rough coils can be scraped back for a smooth finish or left ridged for effect.  

Slab Pots – These are made with rolled slabs of clay by scratching the joined edges, brushing them with liquid clay slurry and fitting the pieces together. The slabs are best prepared by rolling the clay on an absorbent surface using two wooden battens to support the rolling pin. This keeps the clay at an even thickness – essential for a successful pot. The rolled slabs are then left to dry to leather hard, when they can be cut with a sharp knife and ruler to the required shapes. With slab building it is important to let the pot dry slowly to allow the joins to bind securely.  

Using a wheel

Making pots on a wheel is called throwing because the clay is thrown outwards by the force of the rotating wheel head. Perfecting this technique takes a lot of practise and patience. The essence of throwing is controlling the moving clay and at the same time moulding it into the shape required.  

There are two types of wheel commonly used – electric and foot –powered kick wheels. Both originate from the ancient stone or wooden wheels that were spun by an assistant using feet or a stick to provide momentum.  

The ball of clay is squashed firmly into the centre of the dry wheel head. Centering the clay is the first essential in throwing. The hands are always kept wet enough to prevent clay from sticking to them but not so wet as to allow the clay to slide out.  
By keeping the hands firm a dome of clay is made that does not wobble from side to side. Once the clay has been centered the thumb is pressed into the middle of the dome and supported at both sides with the fingers. Then, using the dominant hand to push the clay up from the inside of the forming pot, the other hand is used to push against the outer side wall of the pot.  

The top of the pot may become uneven and it can be trimmed while the wheel is turning by using a potter’s needle held steadily against the soft clay at the desired height. Excess water and loose clay can be sponged off while the wheel is turning slowly.  
The pot is cut off the wheel head by drawing a piece of cutting wire backwards and forwards under the pot. A splash of water on the wheel head will then make it possible to slide the thrown piece gently off, to be put aside to dry.  

Turning

When the pot has dried to leather hard it is placed up side down on the centre of the wheel head and secured with small pieces of soft clay which can be taken away later. With the wheel turning slowly and a turning tool held firmly over the base of the pot, excess clay is scraped away to make a foot or just to even up the thickness of the base.  

The pot is now ready for final drying in preparation for the biscuit firing.  
Pottery is never as easy as it looks and beginners must expect a percentage of failures. However, the disappointments are always surpassed by the satisfaction of success.  

Decoration

Some decoration is best done before the ‘leatherhard’ stage and others when the raw clay has dried out completely.

Colour – the most fundamental decoration is to change the colour of the clay and almost every colour imaginable is made possible by mixing body stains to the clay. Prepared stains and colours are compounded from raw pigments (colouring oxides), which can also be used alone to colour the body clay with more unpredictable results.

Coloured clay can be used for marbling by blending two or more colours together, for inlays by setting a second colour into another and smoothing the joins, and in ‘bas relief’ by joining a sculpted addition to the outside of a pot.

Sculpture and sgraffito – A leather hard pot can be incised, have shapes cut from it, or have its rim pinched up to a crinkly edge. The surfaces of a pot can be sculpted to create a three dimensional effect using a sharp knife or sculpting tools. Texture may be added with almost any object, from a toothbrush to a pattern stamp.
Another method of decoration is sgraffito, whereby a design is drawn on to a leather hard pot with a pencil and then scratched on by following the pattern with a pointed tool. In fact most things are possible as long as the pot does not dry out too much – a quick spray of water prevents this from happening.

Burnishing – A particularly nice effect achieved by polishing the leather hard clay with the back of a spoon or a very smooth stone. This gives a lovely shine to the finished pot after firing.

Applying slip – Slip is coloured clay that is added to the body when it is leather hard. It can be painted on with a brush, trailed on using a ‘slip trailer’, dabbed on with a sponge, stamped on with a template made to any shape or the whole pot can be slightly dipped in the liquid. It is also possible to use the sgraffito method as decoration through a layer of slip that has been previously applied, in order to highlight the colour of the clay beneath.
Slip needs to be the consistency of single cream and is bought ready made to match the clay body that is being decorated, although some potters do make their own by mixing clay with body stains and water.

Biscuit firing – Biscuit or bisque firing means heating the finished pots in preparation for glazing. This first firing dries out and hardens the clay while leaving it absorbent enough to hold the glaze. The process must be taken slowly over about ten hours – too fast and the clay explodes. The kiln is then left to cool slowly before it is opened. This can take up to 24 hours. All the water in the clay evaporates at about 500ºC and as a result the pots shrink a little during the firing.

Decoration on biscuit ware – When the pots have been fired and cooled they can be decorated with designs, patterns and pictures using a wide range of under glaze colours. These are either mineral oxides mixed with water and painted or sprayed on, or prepared colours which are sold in tubes, as felt pens or pencils. A transparent glaze is applied once the colour has dried.

Glaze and Glazing – Glaze is a type of glass that sticks to the clay. Glaze can be bought ready made or made up from a mixture of silica (to make it glassy), alumina (to give it body), flux (to make the minerals melt and blend together), colour and water. Depending on the recipe used glaze can be glossy and smooth, dry and crackled, buttery or any mixture the potter chooses.

Different glazes are necessary for earthenware and stoneware clay as each glaze is designed to match the body of the pot and the temperature to which it is to be fired. Colours in earthenware glazes tend to be stronger than in stoneware.
Only the imagination limits the possibilities for glaze decoration. Sponging, dabbing, spattering with the bristles of a stiff brush are all possible. Pots can be dipped completely or partly in glaze, liquid glaze can be poured over them, glaze can be applied with a brush or trailed over the surface using the same technique as slip trailing, or it can be sprayed on using a house plant sprayer or spray gun. Areas can even be masked out with paper or wax or leave them unglazed.

Glaze firing – Pots ready for glaze firing are placed in the kiln on shelves which are then separated by props that support another shelve above. The bottom of the pots must be wiped clean of glaze where they will come into contact with the shelves, or they will stick. For the same reason pots must not touch each other and space is also left beside the kiln walls to allow the heat to circulate.

Once packed and closed the kiln can then be fired to the desired temperature as quickly as possible. Unlike biscuit firing there is no risk to the pots cracking from being fired too quickly. However, there is a possibility that they will crack if they are cooled too suddenly.
Some glazes, particularly stoneware ones, can be unpredictable and it doesn’t pay for a beginner to become too attached to a pot prior to firing until they have mastered as many variables as possible.

Raku – The kiln used for Raku is usually simple, consisting of a small chamber made from fire bricks or a steel drum lined with ceramic fibre, with an inlet for air, a gas burner at the base and a moveable lid that can act as a flue as well as aiding quick unpacking. From putting the glazed pot in the kiln to holding the finished product can take as little as an hour.

The clay used is course and porous, in fact even after firing the pot remains porous. The pot is made and biscuit fired in the usual way and then glazed with a Raku glaze which consists of a lead substitute, a small amount of clay and colour.

The kiln is preheated until it is glowing with an orange red heat and the pot is placed inside, the optimum temperature is reached when the glaze appears glossy all over. Once the pot has been removed it is plunged into a bed of sawdust and shavings and covered to prevent the wood chips from bursting into flames. After about ten minutes the pot is lowered slowly into a container of water where it boils and seethes. A few minutes later the finished pot is scoured of its sawdust coating to reveal an object that bears all the marks of the forging and alchemy that it has just endured.  

Anyone who participates in Raku firing and is prepared to endure the heat, smoke, and smell and the inevitable failure of imperfection and cracked pots that sometimes occur, cannot help but be excited by it and perhaps hooked on pottery for life.

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