Why pouring boiling water straight into your favourite mug could be shortening its life, according to potters

Amelia Foster • December 10, 2025 16:49

Steam curls out of the kettle, the radio mumbles in the background, and your hand reaches automatically for that mug. The one that fits your fingers, that has a tiny chip on the base you could recognise in the dark. You pour straight from the boil, watch the swirl, and only later notice the faintest new line along the glaze, like a spider’s thread.

Potters notice those lines immediately. They also notice the quiet “ping” a mug sometimes makes cooling on the draining board, and the way hairline cracks creep out from the base after a winter of very hot tea. For them, it’s not just bad luck. It’s physics meeting habit.

This isn’t about wrapping handmade pieces in cotton wool or never enjoying a proper hot brew. It’s about how a small tweak-what you do in the 30 seconds between the kettle boiling and the water hitting the mug-can mean the difference between ten years of use and a sudden, soggy failure over your lap.

Ask studio potters and they’ll tell you the same thing: most mugs don’t die in the dishwasher. They die in the moment boiling water hits cold ceramic.

What really happens when you shock a mug with boiling water

Ceramic looks solid and calm, but on the inside it’s a network of minerals, tiny pores and glassy glaze. When you pour water straight off the boil into a room‑temperature mug, you force all of that to move at once.

The inside of the mug expands quickly as it heats up.
The outside, still cool from the cupboard, lags behind.
The glaze and the clay body expand at slightly different rates.

Those differences sound small, but they add up. The clash in expansion puts the mug under stress-what potters call thermal shock. Thick rims, sharp angles and dense clay feel it most.

A mug rarely “just cracks for no reason”. It usually cracks for the same reason, repeated hundreds of mornings in a row.

Sometimes the shock is dramatic: an audible crack, tea on the counter. More often it’s quiet: microscopic fractures that slowly link up over months, showing first as fine lines in the glaze.

Why some mugs cope and others don’t

Two mugs can look almost identical and behave completely differently with boiling water. The difference is hiding in how and from what they were made.

Clay, firing temperature and thickness

Stoneware (fired hot, often 1200–1300°C) is usually more dense and better at handling heat.
Earthenware (fired lower) is more porous and often more fragile under sudden temperature swings.
Porcelain can be strong but sometimes more sensitive to shock if made very thin.

Thick‑walled, chunky mugs heat unevenly-hot interior, cold exterior-so stresses can be greater. Very thin ones can cope better if the clay and glaze are perfectly matched, but that’s a big “if” outside carefully controlled production.

Handmade vs mass‑produced

Handmade mugs often have:

Slight variations in wall thickness.
Unique glaze mixes and layering.
Foot rings and handles attached by hand.

That’s part of their charm, and also why potters are more cautious about boiling water. Factory mugs are designed for uniformity and often tested against thermal shock, but they’re not invincible either-especially if there’s a gold rim, decal or hairline already present.

Glaze fit matters too. If the glaze naturally wants to shrink more or less than the clay as it cools after firing, it’s already “arguing” with the body. Add boiling water shock every day and something eventually gives.

The quiet warning signs potters look for

Most mugs don’t fail out of the blue. They leave clues.

Crazing: a fine network of crackle lines in the glaze that you can see but not (yet) feel. It looks pretty but signals stress.
Hairline cracks: single, longer lines you can sometimes feel with a fingernail, often running from the rim down or around the base.
Pinging sounds: tiny “tink” or “ping” noises hours after washing or pouring-glaze adjusting and micro‑cracking as it cools.
Sweating or dark patches: staining seeping into the clay body around a crack, especially with earthenware.

If you can see a line inside the mug that lines up with one outside, the crack is talking to both sides. That piece is on borrowed time.

None of this means you must bin a beloved mug on sight, but it’s a nudge to treat it more gently-and to keep an eye on anything you drink from daily.

How potters actually want you to pour hot drinks

The fix is rarely “never use boiling water”. It’s “give the mug half a chance”.

Let the kettle rest

Tea experts in the UK already suggest letting freshly boiled water sit for a minute or two-especially for green, white or delicate teas. Potters quietly agree.

After the boil, wait 60–120 seconds.
In that time, water usually drops a few degrees-still comfortably hot for black tea, far kinder to ceramic.
Use the pause to grab the tea, milk or biscuit; make it a habit, not a fuss.

Pre‑warm the mug

A tiny step that does a lot of work:

Swirl in a little hot tap water or a splash from the rested kettle.
Empty it, then pour your drink.
For very cherished, handmade mugs, do this every time.

The aim isn’t a hot mug, just a mug that isn’t jumping from cold cupboard to boiling shock in one move.

Avoid extreme temperature swings

The fastest way to retire a mug early:

From fridge or freezer straight to boiling water.
From dishwasher end‑cycle (very hot) straight under cold tap.
From cold sink water straight under a boiling kettle.

Ceramics dislike sudden change more than high heat alone. Keep the changes gradual and most mugs shrug and carry on.

When a crack is more than “character”

We all have a mug we’d keep on a shelf just to look at. The issue is when “quirky crackle” crosses into “not great for actual drinking”.

Fine crazing on the outside only: usually cosmetic, but can stain.
Deep or wide cracks you can feel inside: tea and washing water can seep in and out, harbouring bacteria over time.
Leaks at the base: a sign that the crack has gone through the body. Retire it from liquids; use it for pens, brushes or small plants instead.
Visible chips on the rim: tiny, sharp edges against lips and tongues. Not worth the risk.

If a mug was made with unknown or very old glazes, deep cracks can also raise questions about what might leach out into hot liquid. Studio potters working today tend to use food‑safe formulations, but if you’re unsure about a thrift‑shop find, treat it as decorative.

Simple mug‑care habits that quietly extend their life

You don’t need a full “mug care routine”. A handful of small habits go a long way.

Store mugs somewhere they’re not icy‑cold and damp if you can; avoid open shelves directly above a draughty window.
Don’t stack heavy mugs into one another so tightly that rims bang or chip.
Hand‑wash very fine, handmade or visibly crazed mugs with warm-not scalding-water and a soft sponge.
Skip harsh scourers over decorated surfaces, gold rims, decals or hand‑painted details.
Notice new lines or pings; if a mug is clearly deteriorating, demote it gracefully before it chooses the moment for you.

There’s a quiet satisfaction in rescuing a mug earlier rather than sweeping it up later.

Quick comparison: how different mugs handle heat

Mug type	Heat tolerance (typical)	Best everyday habit
High‑fired stoneware	Generally robust, good with hot drinks	Let kettle rest 1–2 minutes; avoid freezer‑to‑boil
Earthenware	More porous, less shock‑resistant	Always pre‑warm; use water just off the boil
Fine porcelain / bone china	Strong but can be thin and ping‑prone	Gentle pre‑warm; avoid sudden cold–hot switches

These are broad trends; individual pieces can behave differently depending on the maker. When in doubt, err on the kind side.

A small pause that changes more than you think

Letting the kettle sit, swirling a splash of warm water round the mug first-these sound like fiddly extras until they become muscle memory. After a few days, the pause doesn’t feel like waiting; it feels like your brew having a short, civilised prelude.

Talk to potters and you’ll hear a similar refrain:

“Mugs don’t mind heat. They mind surprise.”

If a 60‑second habit means your favourite mug sees another decade of mornings, it earns its place next to the kettle. The tea tastes the same. The mug lasts longer. And you’re not left one Tuesday in January, half awake, watching a crack creep through your favourite handle as the steam curls away.

FAQ:

Do I really need to stop using boiling water entirely? No. Just avoid pouring at a furious rolling boil into a cold mug. Let the kettle settle briefly, especially for handmade, earthenware or fine porcelain pieces.

Is crazing dangerous or just cosmetic? Light crazing is mainly cosmetic, but deep, stained crackle inside a mug can trap residue and bacteria. If it’s badly crazed inside, retire it from daily drinks.

Are microwave and dishwasher actually safer than the kettle? They can still stress a mug, but they heat more gradually than a sudden boiling pour. The sharpest shock usually comes from that straight‑from‑the‑boil splash into a cold vessel.

How can I tell if a mug is stoneware or earthenware? Stoneware often feels denser and rings with a clearer “ting” when tapped; earthenware can sound duller and chip more easily. When buying from a potter, ask-they’ll usually label it.

Should I avoid handmade mugs if I drink very hot tea? Not at all. Just treat them as the potter hoped you would: pre‑warm them, pause after the boil, and avoid extreme temperature swings. That way, the story in the glaze is years of use, not one sudden crack.