What food safety really means in a pottery kitchen

"Food safe" isn't a single stamp you can apply to a finished pot. It's a property that comes from three things working together: a well-fired clay body, a glaze that locks everything in, and a surface that stays smooth and intact through years of daily use. A mug can be beautifully thrown and beautifully glazed, and still be wrong for hot coffee if the glaze is under-fired or starts to craze after a month of dishwasher cycles.

The real concerns are leaching, where metals from a glaze dissolve into acidic food; porosity, where liquids seep into the body and harbour bacteria; and physical traps such as chips, cracks and rough patches. Lead and cadmium get most of the attention, rightly, but they aren't the whole story.

Start with lead-free, food-grade glazes

Lead glazes are the classic reason for caution: cheap, glossy, easy to melt, and genuinely harmful when they leach into food over years of use. For any pot that will touch food or drink, work with glazes formulated as lead-free and cadmium-free.

• Buy commercial glazes labelled food safe and keep the label or data sheet. In the UK market, look for glazes that state conformity with lead and cadmium release limits for ceramic ware.
• Treat old recipe books with care. Many pre-1980s recipes assume a lead frit or lead bisilicate. Don't swap in a modern frit without checking the chemistry.
• Be cautious with lustres, gold and platinum, and with metallic decorative glazes. Keep them off the lip, the interior, and anywhere a spoon will scrape.
• When mixing your own, keep a written recipe with accurate oxide percentages. Colourants such as copper, cobalt and iron are generally fine in a stable, well-fired glaze on a durable body — the risk lies in soluble or unstable materials.

Fire to maturity, not just to "looks shiny"

A glaze can look perfect and still be under-fired. Immature glazes are more soluble and more likely to release ions into food, while the body beneath stays open and absorbent. The fix is simple in principle: fire the clay and glaze to their maturity point, and hold them there.

• Match your clay's top temperature with your glaze's range, and use cones or your kiln's thermocouple honestly, accounting for hot and cold spots.
• Add a soak — say 20–30 minutes at the top of the firing — to even out the melt.
• Cool slowly, especially through 700–500°C, to reduce stress and crazing.
• If you want numbers, test water absorption. Weigh a fired shard, boil it for an hour, cool it under water, then re-weigh. Anything above roughly 2% absorption is best kept for decorative use.

Crazing, chips and rough surfaces

Crazing is the fine web of cracks that appears when the glaze contracts more than the clay underneath, or when the pot cools too quickly. The cracks are tiny, but they're open pathways: tea and coffee stain them, and bacteria can settle in them.

• Reduce crazing by adjusting the glaze towards less thermal expansion — a little more silica, fewer alkalis — or by slowing the cooling.
• Keep food-contact surfaces smooth. A well-melted matte is fine; a gritty, pitted or heavily textured interior is not. Think about how it will feel, and how it will clean.
• Glaze the interior of anything that holds liquid, and glaze over the rim.
• Retire cracked, chipped or crazed pots from food service. They make excellent planters, brush pots and studio jars.

Equally, be wary of unglazed rims, coarse grogged footrings and dry, chalky patchiness. A rough surface in the kitchen is a cleaning problem waiting to happen.

Test your pots, then live with them

Testing doesn't need a laboratory. Leave a wedge of lemon or a splash of vinegar in a bowl for 24 hours and look for dulling, colour change or pitting on the glaze. Use a lead-test swab on a spare tile from the same glaze batch. Put a test piece through your dishwasher twenty times and inspect it carefully. Keep a glaze and firing log so you can repeat what worked and set aside what didn't.

In everyday use, avoid thermal shock: no moving an earthenware dish straight from the freezer to the oven. Don't microwave pots with metallic decoration. Wash crazed or vintage pieces by hand, and let hot dishes cool before they meet cold water.

Making and selling with confidence

If you sell or gift your work, be clear about what each pot is for. A decorative raku vessel, a low-fired sculpture and a stoneware mug all deserve different labels. Tell your customer whether something is food safe, dishwasher safe, or decorative only — and explain why. That honesty is part of the craft, and it's what keeps people coming back to your stall.