# Reading What a Test Tile Tells You

Unit: Studio Mastery & Chemistry
Topic: Making and Interpreting Test Tiles
URL: https://claybook.studio/learn/reading-what-a-test-tile-tells-you/

# The Test Tile Is a Data Point

Once fired, a test tile gives you a permanent record of how a glaze behaves. Learning to read it accurately is the key skill.

## What to Look For

**Colour**: Does the fired colour match your expectation? Glazes often look very different wet vs fired. A brown glaze slop can fire to a rich teal. Always test before assuming.

**Texture**: Is the surface glossy, satin, or matte? Crawled, pitted, or smooth? Does it have the depth you wanted?

**Movement**: Did the glaze run? How far? A glaze that runs 5 mm on a vertical tile will run significantly more on a tall pot. If there is any movement, keep the glaze away from the foot ring.

**Thickness effects**: Thick areas and thin areas of application will fire differently. Thick glaze pooling in texture grooves often produces richer, darker results. Thin areas over texture may look washed out.

## Layering Tests

If you want to test how two glazes look layered over each other, use the same tile. Apply the base glaze over the whole tile, then apply the second glaze over half of it. Fire. Now you can see both the base glaze alone and the combination in a single test.

## Building a Glaze Library

File your test tiles with a label on the back: glaze name, recipe source, clay body, cone, and date. Over time your collection becomes a physical library of every glaze result you have ever achieved: one of the most useful references in any studio.

## Keep Exploring

Building a glaze library through test tiles is a practice central to [studio pottery](https://en.wikipedia.org/wiki/Studio_pottery) worldwide. The layering tests described here are a simplified version of the line blend and triaxial blend methods used by glaze chemists to systematically explore how different [glaze defects](https://en.wikipedia.org/wiki/Glaze_defects) and surface qualities emerge across a range of compositions.

## A Simple Review Workflow

After each test firing:
*   Sort tiles by clay body, then by cone.
*   Flag unstable glazes immediately (running, pinholing, crawling).
*   Record next-step actions: retest thinner, retest hotter, adjust silica, or reject.

## Pro Tip

Treat every tile as data, not decoration. The faster you decide what each tile means, the faster your glaze quality improves.

## Check your understanding

### Question 1: How can you test two glazes layered together efficiently on a single tile?

- [ ] A. Fire two separate tiles, one with each glaze, and compare them side by side
- [x] B. Apply the base glaze to the whole tile, then the second glaze over half: one firing shows both results
- [ ] C. Mix both glazes together in one bucket before applying
- [ ] D. Apply glazes in alternating diagonal stripes across the tile

Tip: Apply the base glaze over the whole tile, then apply the second glaze over only half of it. After firing, the tile shows both glazes individually and in combination on the same test.

### Question 2: What information should you record on the back of every test tile?

- [ ] A. Just the glaze name: other details can be recalled from memory
- [x] B. Glaze name, recipe source, clay body, cone, and date
- [ ] C. The kiln shelf position and the batch number of the firing
- [ ] D. Nothing: test tiles should remain unlabelled to avoid confusion with production work

Tip: Label each tile with the glaze name, recipe source, clay body, cone, and date. Over time this collection becomes a physical glaze library: one of the most useful references in any studio, showing you exactly what every glaze achieves under the specific conditions of your kiln.

### Question 3: A glaze repeatedly runs to the base on test tiles. What is the best immediate studio action?

- [ ] A. Use it only on larger forms where gravity has less effect
- [x] B. Flag it and retest with thinner application or adjusted recipe before production
- [ ] C. Increase dip time so coverage becomes more even
- [ ] D. Move it to the hottest kiln zone to stabilise movement

Tip: Flag the glaze as unstable for full-piece use, then retest with thinner application or adjusted chemistry before using it in production. Ignoring run behavior risks kiln shelf damage.