A tetsubin and a tetsu-kyusu look like the same object. One of them cracks on the stove.

They look like the same object. One boils water. Putting the other on heat destroys it. Nambu ironware is sold worldwide under one loose word, so people buy a teapot and use it as a kettle. This page is the difference, and how to tell in one look.

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The two objects

Why this keeps happening

Most overseas listings show only the outside, where the two are near-identical, and many use “tetsubin” loosely for both. Buyers put an enamel-lined kyusu on a stove, or buy one expecting the iron-supplement effect it cannot give.

What follows from it

• ✗Neither damage is a household fix. A cracked lining cannot be relined at all, and rust that has pitted bare iron needs a professional rather than a scouring pad. This is a decision you make once.
• ✓Bare iron must be dried after every use. An unlined interior rusts if left wet. The lined version does not ask this of you, which is the trade it makes.
• ✗No amount of tradition changes the lining. Age, provenance and a hand-cast arare pattern say nothing about what is on the inner face. A modern unlined kettle adds iron; a century-old lined teapot does not.

A kettle — listed as unlined, direct heat ↗A teapot — listed as coated, never on heat ↗

Where to look

Nambu ironware is made by long-established foundries in Iwate — Iwachu, Oigen and Oitomi among them. Whichever you buy from, the same question applies first: is the interior bare iron or enamel? Listings often show only the outside.

Oitomi — iron kettles ↗Hitachiya USA — Nambu tekki ↗

Two listings that answer the question

Most listings do not say. These two do, which is the only reason they are here — both are made by Iwachu, and each states its own lining on its product page. They are worth reading side by side even if you buy neither, because they show the confusion in its plainest form: the second one is sold under the word tetsubin and then tells you not to put it on a flame.

• ✓The kettle. Its title says No Enamel, Direct Fire, and the material field gives cast iron, black-baked inside and out — bare metal, not a lining. This is the one that boils water and gives you iron.
• ✗The teapot. Sold as a Tetsubin Teapot, but its own bullets read the interior is coated and avoid use over a direct flame. For steeping only. It will not add iron to anything.

A kettle — listed as unlined, direct heat ↗A teapot — listed as coated, never on heat ↗

Amazon listings change under the same address, and sellers relist. Whatever you are looking at, check the material or interior field on the page in front of you before buying — that field, not the product name, is what tells you which object it is.

Or the whole shelf

If you would rather compare than be pointed at one piece, the search below is the one worth using. It is narrow on purpose: searching for a cast iron teapot returns a wall of enamel-lined pots, while this wording brings the Iwate foundries — Iwachu, Oigen, Ikenaga, Itchu-do — up into the first screen. Two things to expect. The first few results are paid placements and are usually not ironware at all, so scroll past them. And the same check still applies to every listing you open: find the material or interior field, and if it is not stated, that silence is your answer.

Nambu ironware on Amazon — the whole shelf ↗

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