Calcium Carbonate in Pottery: What It Does and Why It Matters
When you think of calcium carbonate, a naturally occurring mineral compound used in ceramics to control glaze flow and stabilize clay bodies. Also known as limestone or chalk, it's one of the most common additives in ceramic recipes, even if most potters never label it as such. You might picture antacids or chalkboards—but in pottery, it’s doing something far more essential: helping your glaze melt just right and your clay survive the kiln without cracking.
Calcium carbonate isn’t just filler. It’s a flux, meaning it lowers the melting point of other materials in your glaze, like silica and feldspar. Without it, many glazes would stay powdery and dull at typical firing temperatures. But too much, and your glaze runs like melted plastic. It also helps stabilize the clay body by reducing shrinkage and preventing warping during drying and firing. That’s why it’s often mixed into earthenware and stoneware clays—even when the recipe doesn’t list it outright. You’ll find it hiding in ball clay, whiting, and even some commercial dry glaze mixes.
It’s not just about chemistry. Potters use calcium carbonate to tweak surface texture, too. A small amount can create subtle matte finishes or encourage crystal growth in certain glazes. Some artists even add it deliberately to create unpredictable, organic effects during reduction firing. It’s a quiet player, but it shapes the final look of your work more than you think. And while it’s not a magic fix, understanding how it interacts with other materials helps you troubleshoot glaze defects, fix pinholes, or adjust your recipes without guessing.
What you’ll find below isn’t a textbook on ceramics. It’s a collection of real, practical posts from potters and ceramic chemists who’ve wrestled with glaze runs, clay cracks, and firing inconsistencies—and figured out how calcium carbonate was the hidden variable. Whether you’re a beginner trying to stop your mugs from exploding in the kiln or a seasoned potter fine-tuning a new glaze, these guides cut through the noise and show you exactly what works.
