Tips for Walker clay bodies

The following hints may prove helpful to some potters, especially those with no previous experience of Walker Ceramics clay bodies. Comments refer to both stoneware and earthenware clays unless otherwise stated.

Ageing will dramatically improve the working qualities of any clay therefore it is an advantage to keep a 3-6 month supply on hand, if space and finances permit.
All Walker Ceramics clay bodies are extruded through porcelain and de-airing stainless steel pugmills. This eliminates the need for time consuming preparation before throwing. As a block is cut into pieces of the required size each ball can be formed by gentle kneading on a clean bench top. Lengthy time in kneading on an absorbent surface is only necessary if the clay is too soft. When reclaiming leftovers, the clay should be kneaded for a short time and then wedged until even in consistency. Faulty wedging can be the cause of splits, bloats or cracks that can occur on any part of a pot during throwing, drying or firing.
Air pockets can cause splits, cracks and bloats. These are easily noticeable during throwing – clay with any air pockets should be re-wedged – however if only one or two appear in a pot they can be pierced with a pointed tool to allow the air to be gently pressed out with the fingertips.
S” Cracks: To eliminate “S” cracks from the base of the pots (this occurs mainly with open stoneware clays), the following hints could prove helpful. When centering, the clay should be formed into a cone as high and as narrow as possible and then pressed onto the wheel head into a flat perfectly centered ball. This practice, like wedging, helps to even out consistency and also arranges the small particles into a spiral that gives extra strength when the ball is opened out into a cylinder. Next the base must receive the same amount of compression as the walls. So when the ball is opened out the fingertips should be run over the base firmly several times before further attention is given to the sides. Any water in the bottom of the pot should be removed as soon as possible. If allowed to collect there and saturate the thin base, star and “S” cracks can result.

When compressing the base, an effort should be made to eliminate the small “nipple” of clay that can form in the centre of the base as this is usually the cause of small “S” cracks. The thickness of the base is also crucial. A good guide is to make the base of even the largest pots as thin as possible. As soon as the ware is firm enough it should be turned. After the necessary amount of clay has been turned out of the base, it can be further compressed from the outside (care should be taken not to press your fingers right through). However, the tension resulting from pressing the base slightly inwards (especially on closed in forms) will give extra strength and further eliminate the possibility of “S” cracks.

Drying: Finished pots should be dried upside down or on their sides out of draughts or direct sunshine. Too quick or uneven drying can cause distortion and cracks. (Special attention must be given to the Feeneys Clay range in this respect while on the other hand No.10 and PB103 hardly ever suffer from forced drying.) To avoid warpage, flat ware (bowls, platters, etc) should always be thrown on batts and not handled until dry enough to turn.
Throwing “off the hump” may be a problem with most stoneware bodies, however No.10 Stoneware, Feeneys White Stoneware and PB103 have proved quite successful . This technique makes it impossible to give the base the necessary compression, thus causing losses due to “S” cracks. For the same reason, goblets with solid stems in most stoneware bodies could prove to be a disappointment. Appendages such as knobs, spouts, handles, etc. should be attached as soon as the bases are turned. Both surfaces should be roughened, then water or slip of the same clay applied before the parts are pressed firmly together and finally modelled to give a neat appearance.
Knobs are frequently turned from the “waste” clay leftover from bowl-shaped lids. This practice can cause “S” cracks across large bulky knobs. To overcome this problem, knobs can be thrown from a small ball of clay attached to the lid in the usual manner, yet even thrown knobs can cause problems – if air is trapped between the knob and the lid, the knob can fall off during either drying or firing. A small hole drilled from the inside of the lid into the knob is a good safety measure.
Unusually long and fine handles tend to dry out and shrink long before the pot that they will be attached to. To avoid broken handles a thin strip of plastic should be wrapped around them – this will even out the drying. The plastic can be left in position until the bisque firing.
Over-sponging ware during throwing will expose silica / grog and result in an unpleasant sandy finish – this can be annoying on the rims of drinking vessels as well as possibly causing shelling of glazes. By finishing off edges with a small piece of chamois, a smooth finish will result.
Bodies such as White Pottery, White Earthenware, White Midfire, Superior White Porcelain, No 10, Feeneys White Stoneware and PB103 are all suitable for fine work because their small particle size giving a smooth finish.
Turning can also cause a rough finish but this can be smoothed out by running a modelling tool or thumbnail over the pot while it is still rotating on the wheel.
Marbled and striped effects are usually achieved by wedging bodies of different colours together. The clay thus prepared is rewrapped and allowed to stand for some time before use. However, cracks can occur due to the differences in shrinkage. A safer way of achieving the same results is to use the same body – staining part of it and leaving the rest its natural colour. If correctly wedged, no separation should result using this method e.g. Buff Stoneware (BSW), Red Stoneware (RSW) and Dark Stoneware (DSW) can all be successfully marbled.
Finally, most losses during the bisque fire can be eliminated with a little patience. A rate of 50°C per hour during the early stages of firing and 150°C during the later part is recommended. Also remember pots that are not completely dry or are too heavy are a danger to all other pots around them. To many potters, glazing requires as much care and thought as the actual making of pots. Even the most highly recommended glazes should be tested to see how they behave in your own kiln before being applied to pots.