Choose the inside curve before widening a bowl. A deep rounded form and a shallow open form need different wall support. Work from the lower curve toward the rim so the widening develops throughout the profile.
Plan the interior and foot
Sketch a cross section from the center of the floor to the rim. Start with a modest diameter so you can support the clay as it opens. The line should show where the lower curve begins and how it meets the upper wall.
Leave a base allowance for the foot you intend to trim. The outside can retain some extra clay, but avoid creating a large block below a thin upper wall that will need extensive correction later.
Open the curve gradually
Establish an even wall that can tolerate shaping. Resist pushing the top outward early simply because a bowl needs a wide mouth. If the lower wall remains heavy while the upper wall spreads thin, the two regions will behave differently under further pressure.
Reduce speed as the form opens and becomes less contained. Work gradually from the lower curve toward the rim with paired support. Watch where the shape changes most abruptly. A ledge inside the bowl may need a smoother transition, but repeatedly pressing that spot can create a weak band.
Refine the surface and rim
A curved rib can help refine the interior when its contour suits the intended bowl. Support the opposite surface and use light, controlled contact. A tool with the wrong curve can force the clay into an unintended profile or concentrate pressure on a small area.
Inspect the surface after a pass. If the bowl is soft and swaying, stop refining it. Repeated rib pressure can thin the curve further while the clay has less strength to hold it.
Preserve enough substance at the edge for gentle finishing. A very thin, widely flared rim is vulnerable to distortion when handled. Remove standing water and review the silhouette from the side while the wheel turns slowly. Then let the bowl firm with support rather than lifting it by its opening.
Questions about this topic
Can I turn a cylinder into a bowl?
Yes, but establish an appropriate wall and then open it gradually. Simply pushing the rim outward does not develop the entire bowl curve.
Why does the rim keep folding?
Inspect whether it is too thin, too wet or spreading beyond the support beneath it. Speed and repeated finishing pressure can also contribute.