# Why Test Tiles Are Non-Negotiable

Unit: Studio Mastery & Chemistry
Topic: Making and Interpreting Test Tiles
URL: https://claybook.studio/learn/why-test-tiles-are-non-negotiable/

# Never Trust a Glaze Until You Have Tested It

A test tile is a small piece of fired clay used to evaluate how a glaze looks and behaves before committing it to finished work. No matter how experienced you are, every new glaze (whether a recipe you mixed yourself or a commercial glaze you have never used) should be tested before it goes on a piece you care about.

Glazes behave differently on different clay bodies, at different cone ranges, and in different kilns. A glaze that fires beautifully in one studio may run, crawl, or look completely different in yours.

## What Makes a Good Test Tile

A test tile should:

*   Be made from **the same clay body** you will be using for your finished work.
*   Have a **vertical face** so you can see whether the glaze runs. A flat tile lying horizontally will not show you how a glaze behaves when it is upright on a pot.
*   Have a **foot or base** that can sit on the kiln shelf without the tile being glued to it if the glaze runs.
*   Be bisque-fired before glazing, just like your regular work.

A simple and popular tile design is an extruded or hand-formed rectangular bar with a hole for hanging, a grooved texture on one face, and a slight curve or raised lip at the base to catch glaze drips without fusing to the shelf.

## Explore More

Test tiles are especially important when working with glazes that behave differently across clay types: a glaze that looks beautiful on [stoneware](https://en.wikipedia.org/wiki/Stoneware) may craze or crawl on [porcelain](https://en.wikipedia.org/wiki/Porcelain) due to differences in [thermal expansion](https://en.wikipedia.org/wiki/Thermal_expansion). Systematic testing is what separates reliable studio practice from costly trial and error.

## Test Tile System That Scales

As your glaze testing grows, standardise your tile format:
*   Same dimensions
*   Same texture band
*   Same dip timing
*   Same bisque temperature

Consistency in the tile itself is what makes comparisons meaningful.

## Pro Tip

Fire duplicate tiles when possible. One can be archived and one can be handled during class, sales prep, or studio consultations.

## Check your understanding

### Question 1: Why should test tiles have a vertical face rather than lying flat?

- [ ] A. Vertical tiles use less kiln space than flat ones
- [x] B. A vertical face shows how the glaze runs under gravity, as it would on a real pot
- [ ] C. Glaze applies more evenly to vertical surfaces
- [ ] D. Flat tiles absorb too much glaze and give false results

Tip: A vertical face shows whether the glaze runs under gravity, which is how it will behave on an upright pot. A flat tile tells you only about surface appearance, not flow behaviour.

### Question 2: Why should test tiles be made from the same clay body as your finished work?

- [ ] A. Different clay bodies fire at different temperatures and would give misleading cone information
- [x] B. Glazes interact with the clay body beneath them: a different body may produce different results
- [ ] C. Any clay body works fine: glazes look the same on all surfaces
- [ ] D. It is just a studio convention with no technical basis

Tip: Glazes interact chemically with the clay body beneath them. The same glaze on a different clay body may produce a different colour, texture, or fit. Only testing on your actual clay body gives accurate results.

### Question 3: Why is a standard tile shape important when building a long-term glaze test library?

- [ ] A. It allows you to fire more tiles per shelf layer
- [x] B. It keeps comparisons valid by reducing non-glaze variables
- [ ] C. It ensures every glaze will have the same final color
- [ ] D. It prevents glaze movement on vertical sections

Tip: Standard tile geometry controls variables. If shape and texture vary from tile to tile, visual differences may come from tile design rather than glaze behavior.