What will destroy the piece you already own

Enamel-lined — a teapot (鉄急須). Never on heat.

Do not

• Any direct heat — stove, flame, induction. The enamel and the iron expand at different rates, so the lining cracks and flakes. It is not repairable.

Instead

• Steeping tea with water boiled elsewhere.

The lining also blocks iron contact, so this piece adds no iron to the water — whatever the listing implies.

Unlined — a kettle (鉄瓶). Belongs on direct heat.

Do not

• Leaving it wet. An unlined interior rusts. Empty and dry it after every use.

Instead

• Direct heat, to boil water. This is the version that measurably adds iron.

Because the interior is unlined, the iron meets the water. That is the whole design.

Assume enamel until you know.

Do not

• Putting it on heat. Getting this wrong once is irreversible; waiting costs nothing.

Instead

• Tilt it to a window. Enamel throws a clear reflection, like the inside of a mug. Bare cast iron scatters the light and looks matte.

Most overseas listings show only the outside, where the two are near-identical, and many use "tetsubin" loosely for both.

It is not ready to cook in. Season it first (目止め).

Do not

• Cooking something strongly flavoured in it first. Unglazed clay is porous: it seeps, stains, and holds the smell — and none of that scrubs back out.

Instead

• Simmer a thick rice porridge in it once: cooked rice, fill to about 80% with water, boil on low for roughly 20 minutes, then cool completely. The starch settles into the pores and seals them.

Almost no overseas listing mentions this step. Skipping it does not break the pot — it marks it.

No seasoning needed.

Do not

• Following donabe care advice for it. Porcelain (磁器) is vitrified — there are no open pores to seal.

Instead

• Use it as it is.

This is why the earthenware / porcelain question has to come before any care advice at all.

Season it now. It still helps.

Do not

• Scrubbing harder. The absorbed odour is inside the clay body, not on the surface.

Instead

• The same rice-porridge simmer. It will not lift what is already in there, but it stops more going in.

Sealing the pores makes the interior far less absorbent from that point on.

Real urushi. Treat it as a resin film, not a varnish.

Do not

• Dishwasher. Never. Heat, water pressure and detergent together crack, cloud and peel the film.
• Microwave, oven, direct flame. Immediate and major damage.
• Direct sunlight, including in storage. UV degrades the film itself.
• Soaking, or leaving it to air-dry on its own.
• Stacking without cloth or paper between pieces.

Instead

• Lukewarm water, a soft cloth, rinse, dry immediately.

Every one of these is a normal, reasonable thing to do with Western tableware. Nothing about the object signals otherwise, and none of the damage is reversible.

Unknown. It may be urethane, and the two want opposite treatment.

Do not

• Assuming either way. A urethane-coated bowl is genuinely dishwasher safe; a urushi one is destroyed by the same cycle.

Instead

• Ask the seller which it is. If a listing will not say, treat that silence as the answer and handle it as urushi — the cautious option costs you nothing but hand-washing.

General marketplaces rarely distinguish the two. The word "lacquer" on a label covers both.

Double bevel. Either hand.

Do not

• Nothing about the grind — but check the steel below.

Instead

• Use in either hand. The geometry is symmetrical, so it tracks straight for anyone.

Single bevel — and it is handed. Check it matches your hand.

Do not

• Buying one without checking which hand it was ground for. In the wrong hand the blade is not blunt, it is backwards: the flat face rides the food and the ground face steers the cut away. No sharpening fixes it.

Instead

• A left-handed cook needs a left-handed model. These are usually made to order, take longer, and cost roughly 30% more — which is worth knowing before, not after.

Overseas listings routinely omit which hand a single-bevel blade is ground for. Yanagiba, deba and usuba are all single bevel.

It will rust. That is the trade, not a defect.

Do not

• Dishwasher. Leaving it wet. Leaving it in water. Cutting lemons and other acidic food and walking away.

Instead

• Dry it immediately after use. In exchange it takes a very fine edge, sharpens easily, holds it, and develops a patina.

Carbon steel has no chromium, so a wet blade can spot within minutes. Listings describe it as a performance upgrade and rarely mention this at all.