# Why Clearance Is Everything

Unit: The Final Bake: Glaze Firing
Topic: Loading a Glaze Kiln
URL: https://claybook.studio/learn/why-clearance-is-everything/

# A Glaze Kiln Is Not a Bisque Kiln

After bisque firing, your pots have no glaze on them and nothing sticks to anything. Loading a bisque kiln is relatively forgiving: you can stack pieces inside each other and pack the shelves tightly. A glaze kiln is completely different. **Glaze melts.** Any piece touching another piece, or touching a kiln shelf without a barrier, will fuse permanently.

## The Golden Rule: Nothing Touches

Every glazed surface must have clearance from every other surface and from the kiln shelf. This applies to:

*   **Pot-to-pot**: Two glazed pots must never touch. Even a 2-3 mm gap is enough.
*   **Pot-to-shelf**: The base of every pot must be free of glaze. If glaze runs to the foot, it will bond to the shelf.
*   **Glaze on the bottom**: Always wipe, scrape, or wax the bottom centimetre of every pot before loading. This is non-negotiable.

## Glaze-Load Precheck
Before you start loading:
* Visually confirm every foot is clean and/or waxed
* Group pieces by height to plan shelf spacing
* Set aside any “drippy” glazes for top or sacrificial shelves

A few minutes of planning prevents hours of grinding later.

## Kiln Wash

Kiln wash is a refractory coating brushed onto kiln shelves before every glaze firing. It creates a sacrificial layer that glaze will not bond to permanently; if a glaze drip reaches the shelf, you can chip it off the kiln wash rather than destroying the shelf.

Apply kiln wash in thin, even coats with a wide brush. Let it dry fully before loading. Never apply kiln wash to the underside of shelves or to the kiln walls.

## Go Deeper

Kiln shelves and posts are made from [refractory](https://en.wikipedia.org/wiki/Fire_brick) materials designed to withstand repeated high-temperature firings without warping or cracking. The importance of proper kiln loading becomes especially clear when working with glazes that approach [vitrification](https://en.wikipedia.org/wiki/Vitrification) temperatures, where even small errors in clearance can fuse pieces permanently.

## Common Mistakes and Quick Fixes

*   **Bisque loading habits in glaze firing**: Never stack glazed ware or let surfaces touch.
*   **Skipping bottom checks**: Build a foot-clean check into loading flow.
*   **Treating kiln wash as optional**: Refresh shelves regularly to protect expensive furniture.
*   **Packing too tightly near drippy glazes**: Give high-flow pieces extra space and safer placement.

## Practice Exercise

Before your next glaze load, stage all ware on a table and do a dry-run shelf map by height and run risk. This planning exercise usually increases capacity and reduces breakage in the same firing.

## Check your understanding

### Question 1: Why must every pot have clearance from other pots and shelves in a glaze firing?

- [ ] A. To allow hot air to circulate around each piece
- [x] B. Glazed surfaces fuse together permanently when they touch at firing temperature
- [ ] C. To prevent the glaze from dripping
- [ ] D. It is only necessary for porcelain, not stoneware

Tip: Glaze melts at firing temperature. Any glazed surface touching another surface will fuse permanently to it.

### Question 2: What is the purpose of kiln wash on kiln shelves?

- [ ] A. To improve heat distribution across the shelf
- [x] B. To create a sacrificial layer so glaze drips do not bond permanently to the shelf
- [ ] C. To make the shelf surface smoother for loading
- [ ] D. To prevent shelves from cracking under heat

Tip: Kiln wash is a refractory coating that creates a sacrificial layer so that glaze drips can be chipped off without destroying the shelf.