Keeping stoneware from staining

A mug that goes brown inside after a few months of tea is not wearing out. It is picking up tannin, the same compound that stains a teapot, and it comes back off with something already under your sink. Stoneware asks for very little, but it asks for the right little.

Tea and coffee stains

Tannin sits in the glaze rather than soaking through it, which is why it lifts rather than sets permanently. Rinse the mug straight after use if you can, since a stain that sits overnight is harder to shift than one caught the same day. For a mug that has already gone brown, the baking-soda method works reliably and needs nothing exotic.

1. Make a paste of baking soda and a small amount of water, thick enough to sit on the surface without running.
2. Rub it over the stained area with a soft cloth or the rough side of a sponge, working in small circles.
3. Leave it for five to ten minutes.
4. Rinse well and dry.

For a mug that has gone brown all over, a longer soak in a mix of warm water and a spoonful of baking soda, left for an hour, does most of the work before you need to rub at all. Avoid bleach. It can react with minerals in the glaze and clay body over time, and it is not needed for a stain this ordinary.

Crazing: the fine lines in the glaze

Look closely at a stoneware mug and you may see a faint network of hairline cracks in the glaze itself, most visible when the light catches it at an angle. This is crazing, and it happens because the glaze and the clay body cool at very slightly different rates when the piece is fired, leaving the glaze in a fine web of tension lines. It is not a defect and it does not mean the mug will fail. It is where stains tend to gather first, since the lines give tannin somewhere to sit, which is why a crazed mug can look more stained than an uncrazed one even with identical use. The baking-soda treatment reaches into the lines as well as the surface. Crazing does not get worse with normal washing and does not affect how the mug holds liquid.

Thermal shock

Stoneware is fired at high heat and is sturdy, but it does not like a sudden jump in temperature. Pouring boiling water into a mug straight from the fridge, or plunging a hot mug into cold water to rinse it, can stress the glaze and, in the worst case, crack it. Warm the mug first with a splash of hot tap water, empty it, then pour your tea or coffee. Let a hot mug cool for a minute before you rinse it under a cold tap. The rule is simple: change the temperature gradually, not all at once.

The dishwasher truth

Glazed stoneware generally survives a dishwasher without complaint, and the glaze itself is not damaged by it. What suffers is the finish over time: hard water and strong detergent can leave a mug looking slightly duller after a few hundred cycles, and the water temperature swing on some machines is more abrupt than what your hands would ever do at the sink. Handwashing in warm, not scalding, water keeps a mug looking its best for longest, but a dishwasher will not ruin one. Use whichever fits your evening.

None of this is complicated. Rinse it soon, treat a stain when you see one, warm the mug before you pour, and the pair will look much as they do now for years past the point most mugs are chipped and binned.