# Inside the Kiln: The Supporting Structure

Unit: The First Bake: Bisque Firing
Topic: Kiln Furniture
URL: https://claybook.studio/learn/inside-the-kiln-the-supporting-structure/

# What Holds Your Pots Up

The inside of a kiln is not just an empty oven. It is a precisely arranged structure of shelves and posts (collectively called **kiln furniture**) that holds your pots at different levels and allows heat to circulate evenly around every piece.

## Kiln Shelves

Kiln shelves are flat, refractory (heat-resistant) slabs that pots sit on. They are typically made from cordierite or mullite, materials that can handle repeated thermal cycling without cracking.

*   **Half shelves** are useful for flexibility: you can arrange them at different heights in the same level.
*   **Full shelves** are more efficient for large loads.
*   Shelves conduct and store heat, contributing to an even temperature inside the kiln.

## Kiln Posts

Kiln posts are columns (cylinders or squares of refractory material) that support the shelves at different heights. They come in various heights (typically 1cm to 15cm).

*   You always use **three posts per shelf** (never four). Three points define a plane; four can rock and make the shelf unstable.
*   Posts are placed in a triangular arrangement, usually near the outside edge of the shelf.

## Why Furniture Matters

Kiln furniture directly affects the firing. Poorly arranged shelves restrict heat flow, creating hot and cold zones. Over-loaded shelves can bow and crack. Understanding your furniture is essential for consistent, even firings.

## Furniture Setup Checklist
Before loading pots:
* Verify shelves are level and stable
* Use three-post support pattern per shelf
* Keep element-side clearance for airflow

Stable furniture is the foundation of a safe firing.

## Go Deeper

Kiln shelves and posts are made from the same refractory materials used to build the [kiln](https://en.wikipedia.org/wiki/Kiln) itself, engineered to survive thousands of degrees of thermal cycling. Potters use [pyrometric cones](https://en.wikipedia.org/wiki/Pyrometric_cone) placed among the furniture to verify that heat is reaching every shelf level evenly.

## Check your understanding

### Question 1: Why do you always use exactly three posts to support a kiln shelf, not four?

- [ ] A. Four posts use too much space
- [x] B. Three points define a stable plane; four can rock
- [ ] C. Three posts are cheaper
- [ ] D. It is just a tradition

Tip: Three points define a stable plane. Four points can rock on an uneven surface, making the shelf unstable and potentially dangerous.

### Question 2: What type of material are kiln shelves made from, and why?

- [ ] A. Regular ceramic clay, fired very thick
- [x] B. Refractory materials like cordierite that withstand thermal cycling
- [ ] C. Steel plates coated in clay
- [ ] D. Brick tiles from a hardware store

Tip: Kiln shelves are made from refractory materials like cordierite that withstand repeated heating and cooling without cracking.