# What Is a Closed or Doughnut Form?

Unit: Advanced Throwing Techniques
Topic: Throwing Doughnut Forms
URL: https://claybook.studio/learn/what-is-a-closed-or-doughnut-form/

# Throwing a Form That Closes on Itself

Most thrown pottery is open at the top: a bowl, a mug, a vase. A closed form is one where the walls come back inward and meet at the top, creating a form with little or no opening. Think of a hollow sphere, a teapot body before the hole is cut, or a sculptural closed vessel.

These forms are sometimes called **doughnut forms** when they have a hole through the middle: like a literal torus shape, or **closed forms** or **hollow spheres** when the top is nearly sealed.

## Why Closed Forms Are Challenging

*   You cannot reach inside to support the walls from the interior once the opening becomes very narrow.
*   All shaping must happen from the outside, requiring controlled outward pressure from inside using tools, or gentle pushing from outside using a rib.
*   The form must be structurally sound enough to support itself: wet clay wants to slump outward.

## Closed Forms in Practice

Closed forms are the foundation for:
*   **Teapot bodies** (closed sphere with holes added for spout and lid gallery)
*   **Hollow sculptural pieces**: decorative vessels, ikebana forms
*   **Lidded boxes** when the lid and base are thrown as one and then cut apart at leather hard
*   **Doughnut or donut forms**: fully enclosed toruses used in sculptural and functional ceramics

## Critical Warning: Never Fully Seal a Closed Form

A completely airtight closed form will explode in the kiln. As the temperature rises, the air trapped inside expands. If there is no escape route, the pressure builds until the form cracks or bursts, damaging itself and everything nearby on the shelf.

Always leave a small hole, or pierce one with a needle tool once the form has stiffened slightly. Even a 3-4 mm hole is sufficient to allow trapped air and steam to escape safely.

## Keep Exploring

Closed forms are the foundation of teapot making, one of the most technically demanding areas of [studio pottery](https://en.wikipedia.org/wiki/Studio_pottery). The Japanese tradition of [raku ware](https://en.wikipedia.org/wiki/Raku_ware) tea bowls and the broader [mingei](https://en.wikipedia.org/wiki/Mingei) folk craft movement both celebrate the mastery of form that closed and spherical shapes require.

## Common Mistakes and Quick Fixes

*   **Sealing forms airtight**: Always leave or pierce a vent hole before firing.
*   **Trying advanced closure too early**: Master simple hollow spheres before torus forms.
*   **Over-thinning walls during shaping**: Keep enough wall mass for structural stability.
*   **No drying plan for enclosed forms**: Dry slowly and evenly to reduce stress cracks.

## Practice Exercise

Throw three closed forms with different vent-hole sizes and track drying and firing outcomes. You will quickly learn practical safe vent dimensions for your clay body and workflow.

## Check your understanding

### Question 1: Why are closed forms harder to throw than open forms like bowls?

- [ ] A. They require more clay than open forms of the same size
- [x] B. You cannot reach inside to support the walls once the opening narrows
- [ ] C. Closed forms must be fired at a higher cone than open forms
- [ ] D. The wheel must spin in the opposite direction for closed forms

Tip: Once the opening narrows, you can no longer reach inside to support the walls from the interior. All shaping must happen from the outside, making control much harder.

### Question 2: What common functional pottery form begins with a closed sphere as its starting point?

- [ ] A. A dinner plate: the rim is closed inward to form the raised edge
- [x] B. A teapot body: closed sphere with holes later cut for the spout and lid gallery
- [ ] C. A standard mug: the walls must be closed before handles are attached
- [ ] D. A large vase: a wide opening still qualifies as a closed form

Tip: A teapot body is essentially a closed sphere. Once thrown and closed, holes are cut at leather hard for the spout attachment and the lid gallery. Mastering the closed sphere opens the door to the full teapot-making process.