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Subscriber Extra: Throwing Bowls

rp bowls

Making bowls requires different skills to making cylindrical pots, with perhaps the most significant difference being the switch of emphasis from the exterior outline of the form to the interior surface and shape. Broadly speaking, all forms develop from a narrower diameter than they have in their final form, so where a cylinder grows from a cone shape, a bowl grows from a flowerpot shape.

We can of course make bowls with flat bases, but when making a bowl with a rounded interior form, a second, distinct refining and finishing process is used at the leatherhard stage. The process is known as trimming or turning, and is used to create a ‘foot-ring’ on which the form stands.

Note that the shape of your centered clay needs to vary according to the width of form you intend to make. In the diagram below, the centered dome shape is superimposed over the cross sections of three generic forms.

Throwing a Small Bowl

When you are making wider, open, or shallow forms, the speed of the wheel needs to slow more, and slow sooner, as the form grows, or the centrifugal force can cause the pot to collapse. To make small bowls for cereal, soup, or dessert, or for making tea cups and saucers, use around 350–650 grams of clay. Here I’m using 600 grams. The clay has been centered into a slightly shallower dome, hollowed down to about 12 mm (½ in.) and opened out with a curved base.

With the wheel turning at medium speed, lubricate the wall inside and out and place your fingertips at the base of the inside and outside of the opened ball (1).

Lift the wall upwards into a flowerpot shape (2) . I find the fingertips to be adequate, and more sensitive to subtle variations in thickness, for throwing small bowl shapes. Lightly compress the rim with your fingertips.

Slow the wheel for subsequent pulls. Gently flare the walls outwards and take care not to over-thin the middle (3).

You have reached the final width and height: A ‘V’ shape rises from a curved interior base, sloping outwards gently to the rim like the bell of a trumpet. It is always a good idea to steady and reinforce the rim by briefly using the ‘H’ hold (finger inside, thumb outside, horizontal finger lightly compressing the rim) (4).

Sponge dry the interior then use a rounded rib to form the shape and finish the inside surface of the bowl (5). Press the rib firmly into the center of the bowl, angled slightly in the direction of the wheel’s spin, and slide up into the wall with decreasing pressure to compress the clay and to unify the curve of the base with the wall to create a seamless, continuous shape. Support the wall on the outside with the fingers of the right hand and form a controlling link to the rib with the thumb. Refine the rim as described in step two.

You can’t pick up a shallow open shape with your palms as you would a narrow cylindrical form, but a small bowl with a narrow base that is sufficiently thick for turning can be lifted or slid off the wheel. If the bowl is larger or has a wider and shallower form, throwing it on a bat may be essential.

Sponge dry the wheel head around the pot. Make a deep undercut at the base of the wall, taking care not to distort the interior shape as you do so (6).

Wire the pot off the wheel head and tuck wet, forked fingertips underneath. Lift off (7) and gently place  the bowl on a board. Correct any distortions when the shape is leatherhard.

Many potters prefer to wet the wheel head around the pot and then wire through once or twice. With a push at the base, the bowl should slide off the wheel on to your hand or a bat on a film of lubrication. However, the pot will then be glued onto whatever it is placed on and will need wiring off again later, so this method is only advised when trimming is intended.

Drying

Confusion can arise over the terminology that potters use to describe the condition of the clay. These important terms refer to different stages of the making process that come at crucial stages in the drying cycle. The knack lies in getting the clay to the state you need at a convenient time when you can work with it.

Diagram4

A pot begins to dry from the moment it is made. In a warm, dry, well-ventilated atmosphere, the water evaporates out of the clay much more quickly than in cool, humid, airless conditions. The thin extremities, such as the rim, will dry first. This is indicated by a change in the clay’s color—it begins to lighten. But this is undesirable when there is further work to do on the pot, so ways to even up or equalize the drying must be employed.

As soon as the rim is stiff enough, turn the pot over and allow the base to dry too. With wide shapes thrown on a bat, another clean bat should be placed on the rim and the pot should be inverted, sandwiched between the two bats. Alternatively, pots may be partially covered. A rim can be wrapped or capped with thin plastic—kitchen bin liners are ideal—to slow the drying process. Super-absorbent fireproofing sheet materials can be cut into planks and used as pot-drying boards, which equalize the drying top and bottom. To preserve pots untouched and allow them to dry evenly, use a rigid airtight container or ‘damp cupboard’.

Leatherhard

‘Leatherhard’ is the term most often used to describe the state when clay is stiff but damp, and in a suitable condition for all the remaining finishing processes—applying handles, lugs, knobs and spouts, trimming and turning.

Clay in the semi-dry state becomes more rigid but stays slightly pliable, not unlike thick leather or hide. You can handle the pot safely without distortion, while the material remains moist enough to attach handles and soft enough to carve into. The hardness of clay in the leatherhard state will vary from being soft like cheddar cheese to hard like chocolate. The clay should still be a uniform color.

Trimming

When is a pot ready to trim or turn? It is not easy to give a definitive answer to this question, because the needs of different shapes and sizes of forms, types of clay and wares, and personal preferences of potters are too variable to sum up in a universal rule.

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The answer ‘when it is leatherhard’ is too general. A better rule to apply would be ‘as soon as the pot is stiff enough to work on without it becoming distorted or damaged’. As a general guide, the base area that will be turned should be soft enough to mark with a thumbnail but not so soft that a fingertip will make an impression. The trimmings should have the consistency of grated cheese – when squeezed in the hand, they will just stick together. If the trimmings are crumbly like grated chocolate, the clay is already on the borderline, and if they are like iron filings, it is too dry.

Trimming tools

Trimming/turning tools have a sharp steel edge to pare away the leatherhard clay. Some are all metal with a right-angled blade, others are wire loops—also called ribbon tools—which I prefer. The one I use is a home-made loop of steel banding wire, which can sometimes be found discarded at construction sites.

Planning a trimmed foot-ring on a bowl

Before you begin turning, it is helpful to make a few measurements and marks on the form as a guide to where and how much to turn.

Set the bowl upright on a flat surface and hold a pencil or stick upright against the rim. Mark the rim height either with a pen or with your finger (see A in illustration at right) on the pencil. Stand the pencil in the center of the bowl, and line up the near and far rims by eye. The difference between the mark and the rim gives you the base thickness at its thinnest point (B).

Look down the line of the wall from above the rim. Run a finger and thumb down either side of the wall to where it begins to thicken and mark that point (C).

The diameter of the foot-ring will vary according to the shape, width, and style of the bowl, but as a rough guide, it will be between one-third and one-half of the rim’s diameter. Use a pair of calipers to measure this approximately (D). When you begin turning, with the wheel at a medium pace, this caliper measurement indicates the foot-ring width.

Lastly, and most importantly, study the curve and line of the bowl’s interior (E). You are aiming to reflect this in the turning and you should keep it in your mind’s eye throughout the process.

Trimming the bowl

Place your pot as close to center as you can. Use the concentric rings on the wheel head to guide you, but you may still need to adjust the pot’s position. An invaluable trimming technique, tapping into center is the fastest way to center a pot (8). However it is difficult to describe and takes practice to learn and do quickly, so try it with a plastic bowl for a few minutes every session.

Revolve the wheel at a slow/medium speed and hold a steady fingertip level with the base of your upturned pot, keeping it close enough so that the pot brushes your finger on the widest point of its trajectory. Focus the eye on the edge of the base (where the turning is to be done), not on the rim of the pot.

Count ‘1-2-1-2’ each time the pot touches your fingertip to pick up the rhythm.

Tap the pot towards the axis of the wheel on the beat ‘1-2’. Tap slightly in the direction of spin. If the pot is small and light, apply light pressure on top of the pot with a finger of your other hand to act as a brake.

Once centered, stop the wheel and hold the pot firmly with one hand while you press three small coils of clay into place around the rim to fix it to the wheel (9).

Use calipers to mark a light ring on the base for the outer edge of the foot-ring (10).

With the wheel spinning at medium pace, turn a groove to establish the width and approximate depth of the foot-ring (11). Note how the fingers of the left hand bridge the pot and turning tool throughout, acting as a stabilizer. The speed of the wheel should be brisk and you should hold the turning tool firmly at a 3 o’clock position, using the slip tray to brace your forearm.

Now trim the clay from your marker on the wall (C in the illustration above) to the base of the foot-ring, using the memory of the bowl’s internal form to guide you in terms of the curve you want to achieve (12).

Note: When the pot starts getting too dry, the turning tool ‘chatters’ or vibrates on the surface, causing ridges. Dampen the surface with a sponge and continue.

Keeping in mind the thickness of the base you measured earlier, trim inside the foot-ring (13), taking care to continue the curve of the form and giving the foot-ring a similar weight, thickness and quality to the form’s rim. To prevent too much downward pressure against the base, use the tool at a very shallow angle.

Give the pot a functional and neat refinement with a shallow bevel to the inside and outside edges of the foot-ring, smoothing it with a firm fingertip (14).

Before you remove it from the wheel, have a look at the bowl at eye level. Mentally remove the foot-ring and examine the shape. Does it reflect your memory of the interior form accurately?

Now remove the lugs of clay and look at the bowl  (15). Rock it from side to side in your cradled hands. It should feel balanced, not bottom-heavy, its weight evenly distributed. Run a thumb and forefinger down either side of the wall to feel for thicknesses. Compare the interior and exterior curves.

Look at the pot in section, to examine the evenness of the wall (16). Notice how the shape now corresponds inside and out, as well as the subtle but vital increase in weight at the foot-ring and the rim.

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