A test tile is a small piece of fired clay used to try a glaze, slip or firing before using it on real work. Good test tiles stand upright, have texture and an edge, and are made from the same clay as your pots.
What Is Test Tile?
Glazes behave differently on different clays, at different thicknesses and in different kilns, so the photo on a jar or a recipe card is only a guide. A test tile shows you what will actually happen in your own setup. Most potters keep a board or box of labelled tiles as a reference library.
Upright, L-shaped or small cylinder tiles are more useful than flat ones, because they show how the glaze moves on a vertical surface. Dipping one, two and three coats on the same tile shows the effect of thickness, and a little texture or a carved line shows how the glaze breaks over edges.
Always label the back with the clay, glaze, number of coats, cone and date, using an underglaze pencil or iron oxide so it survives the firing.
Put a small catch tray or cookie under test tiles of unknown glazes, in case they run. Testing combinations before glazing a whole set is the habit that saves the most heartache in pottery.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.