How to Avoid Thermal Shock in Clay Cookware

Most clay pots that crack in a home kitchen weren’t badly made. They were heated or cooled too fast. That sudden change is thermal shock, and once you know what triggers it, it’s easy to avoid.

What thermal shock actually is

Clay expands when it heats and contracts when it cools. In a fired ceramic body that movement is tiny, but it’s real. Thermal shock happens when one part of the pot changes temperature much faster than the part beside it. The hot section wants to expand while the cooler section holds it back, and stress builds up inside the wall. If it climbs past what the clay can absorb, the body relieves it the only way it can: a crack, or a clean break.

The gap doesn’t need to be dramatic. A room-temperature pot dropped into a hot oven, or a splash of cold water against a hot inner wall, is enough. Every rule below does the same job: it keeps the temperature difference across the pot small and gradual.

Start in a cold oven and heat gradually

This is the single most important habit. Put the pot (food and all) into a cold oven, then switch the oven on. The pot warms at the same pace as the air around it, so no part of it races ahead of the rest.

Skip the preheat. A room-temperature pot going into a 200°C oven is exactly the mismatch you’re trying to avoid. Because you’re starting cold, add roughly ten to fifteen minutes to a recipe written for a preheated oven, and judge doneness by the food rather than the clock. The guide covers oven temperatures and timing in more detail.

Never pour cold liquid into a hot pot

If you need to add stock, wine or water partway through cooking, warm it first. Cold liquid hitting a hot inner surface chills that surface in an instant while the outer wall stays hot. That difference, right across the thickness of the wall, is one of the fastest ways to crack a pot.

Add hot, or at least warm, liquid, and pour it over the food rather than straight onto bare ceramic. The same caution applies in reverse: don’t run cold water into a pot that has just come out of the oven.

Don’t rest a hot pot on a cold or wet surface

Granite, stone, stainless steel and a wet draining board all pull heat out of the base very quickly. The base cools while the walls are still hot, and you’ve created a gradient without touching the oven dial.

When the pot comes out, set it down on a wooden board, a folded tea towel, or a trivet. Do the same on the hob or worktop. Anything that slows the heat loss and spreads it out keeps the pot stable.

Keep it in the oven unless the piece is made for direct heat

Most clay roasters, ours included, are built for the oven, where heat surrounds the whole piece evenly. A gas flame or an electric hob does the opposite: it drives heat into one spot on the base while the rest stays cool. Induction won’t heat clay at all, since there’s no ferrous metal for it to work on.

Unless a specific piece is described as hob- or flame-safe, cook with it in the oven and nowhere else. Direct flame is one of the most common causes of a cracked base.

Soak unglazed clay before you use it

Natural and unglazed clay is porous, and that porosity is part of how it cooks. Before the first cook of a session, submerge an unglazed pot in cold water for fifteen to thirty minutes so the body draws water in. In the oven that moisture turns to steam, which bastes the food and, just as usefully, helps the walls heat evenly from the inside.

A dry unglazed pot going straight into heat is more prone to stress than a soaked one. Fully glazed pieces have a sealed surface and don’t need soaking. The guide walks through soaking and the first few cooks in full.

Let it cool slowly

The gradient works both ways, so the end of cooking deserves the same care as the start. Lift the pot out, set it on wood or cloth, and leave it to come down in its own time. Don’t plunge it into a sink or rinse it while it’s hot. Wait until it’s near room temperature before it meets water. Cleaning is easier then anyway, especially for unglazed pieces.

If it does crack

A very fine hairline on the outside of a well-used unglazed pot isn’t always the end. Some develop faint surface lines and keep cooking for years. But a crack you can catch with a fingernail, one that runs across the base, or one that weeps liquid means the pot should retire from cooking. Don’t cook food in it: a crack can trap residue and can open further under heat. If a piece fails early, or in normal use, that’s worth telling us about.

Treated with a little patience, clay cookware lasts a long time. Every finish in our cookware range is tested for lead and cadmium migration. You can read the results and the materials detail on the page.