The fine cracks in my glaze — is my piece damaged?

No. That web of hairline cracks is crazing, called kannyū in Japanese, and it is not damage. As a piece cools after firing, the glaze and clay body shrink at slightly different rates, and the glaze relieves the stress by cracking. In Japan it is often tuned deliberately and prized. On Hagi ware it is the whole appeal, slowly shifting the bowl's color over years of use.

How do I know if my pottery is porous or vitrified?

Turn the piece over and feel the unglazed foot ring. If the exposed clay is rough, matte, and slightly thirsty when wet, the body is porous and needs seasoning and careful washing. If the foot is smooth, dense, and rings when tapped, it is vitrified and far more forgiving. The difference comes from firing temperature: porous ware is fired lower, vitrified ware higher.

What is medome and how do I season a new piece?

Medome means "closing the pores," done once before using porous ware so it will not seep, stain, or smell musty. Put the piece in a pot with cloudy rice-rinse water (or water with a spoonful of starch), start it cool, and bring to a gentle simmer for 15 to 30 minutes. Let it cool in the water, then rinse and dry. Vitrified porcelain can skip this.

Can I put Japanese pottery in the microwave?

Be careful. Never microwave anything with gold or silver decoration; the metallic overglaze will spark and scorch in seconds. Porous Bizen and earthenware can heat unevenly and even crack, so keep them out if unsure. Plain glazed porcelain is generally microwave-safe, but check the foot ring first and treat it as porous if the clay there feels rough and absorbent.

Is handmade Japanese pottery dishwasher safe?

Skip the dishwasher for anything special. The heat, high-pressure jets, and harsh detergent are hard on glaze, fade overglaze enamels, and strip gold and silver. Everyday glazed porcelain usually tolerates it, but handmade, gilded, or unglazed pieces should be hand-washed with a soft sponge and mild detergent, then dried completely before storing.

How to Use and Care for Japanese Pottery: Crazing, Seasoning & Microwave Rules

Handmade Japanese tableware behaves differently from a mass-produced porcelain mug. An unglazed Bizen cup, a finely crazed Hagi tea bowl, and a gold-painted Kutani plate each ask for slightly different handling — and a few habits that suit one will quietly damage another. None of this is fragile-museum-object territory; it just helps to know what you're holding before the first wash. The single question that settles most of the care decisions below is whether your piece is porous or vitrified.

First, is it porous or vitrified?

That difference comes down to firing temperature. Earthenware and lightly-fired stoneware — Hagi, a lot of mingei tableware, raw-clay Bizen — are fired roughly 1,000–1,200°C, never fully melt their pores shut, and can absorb well over 10% of their weight in water. Porcelain (Arita, Kutani) and high-fired stoneware reach about 1,200–1,300°C, where the clay vitrifies — the silica and feldspar fuse glassy and seal the body — and water absorption drops below 2%, often under 0.5%.

You can usually tell by hand. Turn the piece over and feel the unglazed foot ring: if the exposed clay is rough, matte, and slightly thirsty when you wet it, the body is porous and needs the care in the next two sections. If the foot is smooth, dense, and rings when tapped, it's vitrified and far more forgiving.

Crazing (kannyū) is a feature, not a crack

The first thing that alarms new owners is crazing — a fine web of hairline cracks across the glaze, called kannyū (貫入) in Japanese. This is not damage. As a piece cools after firing, the glaze and the clay body shrink at slightly different rates; where the glaze has the higher thermal expansion it contracts more than the body underneath and relieves the stress by cracking. In Western workshops that mismatch was long treated as a defect, but in Japan it is often tuned deliberately and prized.

On Hagi ware it becomes the whole appeal. The porous body and crazed glaze let tea seep in through the cracks over years, slowly shifting a pale bowl toward amber — a change the Japanese call Hagi no nanabake (萩の七化け), the "seven transformations." The seven is figurative, a poetic way of saying "many"; tea people simply watched a white bowl mature with use and gave the process a name.

The practical consequence: crazed and porous pieces will stain with use, soaking up tea, coffee, soy sauce, and oils. On a Hagi tea bowl that is the point. On a piece where you'd rather avoid it, rinse promptly and don't leave dark liquids standing in it. Either way, the cracks themselves are sound.

Season porous ware before first use (medome)

Because that porous body drinks in liquid, an untreated piece can seep, stain, or pick up a musty smell. The traditional fix is medome (目止め), literally "closing the pores," done once before you start using a new piece. The starch in the water settles into the open clay and seals it.

A common method:

Put the piece in a pot with the cloudy water left over from rinsing rice (togijiru) — or plain water with a spoonful of flour or starch stirred in.
Bring it up to a gentle simmer, not a rolling boil, for 15 to 30 minutes. Start the piece in cool water and heat them together; dropping cold pottery into boiling water invites thermal-shock cracks.
Turn off the heat and let everything cool down with the piece still in the water.
Rinse and dry thoroughly.

Only genuinely porous ware needs this. Vitrified porcelain (most Arita and Kutani) and high-fired glazed stoneware have no open pores to close, so you can skip it. If a porous piece starts soaking up water again after months of use, just repeat the seasoning.

Washing and drying

Hand-wash by preference. A soft sponge and mild detergent is safest for handmade and decorated pieces. Avoid abrasive scrubbers and scouring powder, which scratch glaze and wear down painted or gilded decoration.
Don't soak unglazed or porous ware for long. Bizen, raw-clay surfaces, and earthenware will drink up water and detergent, which can leave odors. Wash, rinse, and move on.
Dry completely before storing. This is the step people skip, and it's the one that causes mold and musty smells in porous pottery. Let pieces air-dry fully — a few hours upside down on a rack — before putting them away. If a piece has absorbed moisture, leave it out a day.
Skip the dishwasher for anything special. The heat, high-pressure jets, and harsh detergent are hard on glaze, fade overglaze enamels, and strip gold and silver. Everyday glazed porcelain usually tolerates it; handmade, gilded, or unglazed pieces should be washed by hand.

The microwave and oven rules

This is where real damage happens, so it's worth being strict:

Never microwave anything with gold or silver decoration. Metallic overglaze — common on Kutani and on gold-banded (kinrande) ware — will spark and scorch instantly. The piece can be ruined and the metal blackened in seconds.
Be cautious with unglazed and low-fired ware in the microwave. Porous Bizen and earthenware can absorb moisture and heat unevenly, getting dangerously hot or, in the worst case, cracking. If you don't know how a piece will behave, keep it out.
Plain glazed porcelain is generally microwave-safe, but check the foot ring: if the unglazed clay there feels rough and absorbent, treat the piece as porous.
Avoid sudden temperature swings. Don't pour boiling water into a cold, thin bowl or take a piece from the freezer to a hot oven. Thermal shock cracks ceramics regardless of origin.

Living with the patina

The same porosity that demands care is what makes these pieces worth owning: use is supposed to leave a mark. A Bizen cup darkens and gains a soft sheen as it absorbs oils from your hands and table; a Hagi bowl shifts color through its crazing over years. Japanese owners talk about sodateru — "raising" or growing a vessel, the way the seven transformations are something you cultivate rather than buy finished. So the goal of good care isn't to keep a piece looking factory-new. It's to keep it sound — sealed where it should be sealed, dried so it doesn't sour, kept away from the microwave and the dishwasher when it matters — and then to use it often enough that it becomes yours.