Moisture content is crucial when throwing cups and bowls

A very wet cup may feel flexible and easy to push on for several minutes before suddenly slipping out of shape as the wall is moved too far. Conversely, a very dry bowl will not move as easily; edges will not open, joins will not merge smoothly, and the walls will show cracks if the form is moved too far. Moisture isn’t only about whether the clay is wet or dry; it affects how much force the clay can take, and what steps are possible at any given time.

An experiment can be helpful here. Take three pieces of the same clay at three different moisture levels. One should be fresh, another should be allowed to rest until it firms up a bit, and the third should be left to become quite stiff, but still pliable. Apply the same motions to each piece and note the difference. The most flexible piece will be easiest to move. The stiffer piece will be harder to move. Seeing this difference will help you understand why the same action performed at different times may have varying results when making tableware.

It’s common for a very wet bowl or cup to get overworked as you attempt to shape it. The walls can stretch rapidly, the rim loses its shape, and the base may distort as the piece is handled. Adding water with a sponge usually doesn’t help; it often makes the piece more difficult to control. A damp finger can help to refine a surface, but too much water will cause the outer surface to become slick and the clay to lose some strength. If your piece gets flatter and flatter every time you turn it, it’s usually better to lighten your touch or let the clay stiffen rather than attempting to continually reshape it.

Another factor to consider is that different areas of the same piece dry at different rates. A thin rim will dry faster than a thick base, and a handle attached to a cup will dry at a different rate than the cup itself. As these parts dry at different rates, stress can build up around joins and edges. Scoring and slip can help to bind the join together, but moisture content is also important. Attaching a very wet handle to a fairly stiff cup will make the join more difficult to work as both pieces continue to dry.

Once the clay has stiffened a bit (often referred to as “leather hard”), it becomes more useful for refining. A bowl or cup will hold its shape better as the rim, foot, or surface is modified. The clay is too stiff for further shaping, but it is generally easier to work without leaving dents. This point illustrates why the process of making ceramics is often a matter of timing; there isn’t always a single moisture level that works well for all stages of shaping, joining, trimming, refining, and drying.

Before attempting to refine a piece, try pressing the clay gently and noting its response. If the clay stretches easily, don’t apply too much pressure. If the clay is very resistant and begins to crack at the edges, pushing it further won’t help. Fine moisture control may not be as impressive as fine shaping skills, but it’s useful for almost every step of making functional tableware. The easiest rule to remember is to work with the clay as it is now, not as it was a half hour ago.