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 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 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.
