Caring for Japanese Iron Kettles “Nambu Ironware (Sougata Method)”

From Anxiety About Rust to Clarity in Judgment

When you first held your iron kettle, perhaps your heart lifted at its weight and quiet presence.

Yet alongside that joy, a question may have settled in: "What if I let it rust?" The more you search, the more warnings accumulate: "never do this," "always watch for that" until the path forward becomes obscured.

What we offer here is not a list of rules, but a way of seeing. Once you understand the nature of the tool, what is ordinary and what requires attention becomes clear.

The kettles we speak of are made using the traditional fired-clay mold method (sougata), with no enamel coating on the interior. The inside is fired at approximately 900°C over charcoal, forming a protective oxide film of magnetic iron oxide.

*Please note: this guidance does not apply to enamel-finished kettles or those made by other methods.

Setting Aside the Belief That "Rust Means Failure"

Much of what is written about iron kettles assumes a single premise: "avoid rust at all costs." And so, when white spots appear, anxiety follows. When red marks emerge, some stop using the kettle altogether.

What we wish to share is this: once you understand the nature of the tool, what is ordinary and what requires attention becomes clear.

Our aim is not perfection, but confidence: the ability to look at your kettle and know, for yourself, what you are seeing.

White Spots Are Scale: A Gift from the Water

After about ten days of use, white spots may appear on the interior. These are mineral deposits from the water itself, what is called scale.

In regions with hard water, this scale forms more quickly. But it is not deterioration. It is a gift from the water, a natural armor the kettle builds to protect itself. The water it boils becomes softer, mellower.

Do not scrub this white layer away, thinking it "dirt." It is the kettle's own doing, a quiet sign that the tool is maturing in your care.

When Red Spots Appear: The Answer Lives in the Water

Red spots may appear on the interior. When you see them, there is no need to think, immediately, that something has gone wrong.

The question to ask is this: Is the water cloudy? Does it carry a metallic taste?

If the water is clear and tastes as it should, those red spots can be left alone.
If the water shows cloudiness or a metallic note, boil used green tea leaves in the kettle.

The tannins in the tea will react with the iron, forming a dark protective film: tannin iron. This follows the same principle as the craftsperson's finishing process, known as "ohaguro." In this way, you are carrying on the finish, continuing what the maker began.

To understand the depth of this craft, we invite you to quietly observe the meticulous 35-minute creation process by Kamasada's artisans.

Intervention is needed only when the water itself tells you so. Appearance alone is not cause for alarm.

"Let the Moisture Escape" Rather Than "Use It Daily": The Heart of Care

You may have heard "use it every day" as advice for iron kettles. But what matters more is this: not leaving moisture behind.

Iron holds heat well. After use, simply empty the kettle and leave the lid off. The residual warmth will allow the kettle to dry itself.

Rust most often comes from cooling the kettle while moisture still clings inside. At the lid's rim and the spout, capillary action draws water into narrow spaces where it lingers.

The heart of care rests on this single point.

Iron Kettles Have Their Limits: A Quiet Respect for Thermal Rhythm

Cast iron does not tolerate abrupt shifts in temperature. Pouring cold water into a kettle that has been heated dry can cause cracks to form.

Kettles made by the sougata method are especially thin-walled, and ask for gentleness.

More than rust, it is thermal shock: this sudden disruption of the metal's rhythm that poses the greater risk of irreparable harm.

A quiet moment of respect for the tool's nature will serve you far better than haste.

Not Perfection, But Confidence in What You See

What we have shared is not a set of protective rituals, but a way of seeing what is happening now.

White spots are scale: an ordinary, beneficial change.
Red spots, if the water remains clear and clean, need not concern you.
Moisture allowed to escape means rust has little foothold.

What matters is not maintaining an ideal, but moving forward with confidence: knowing that you can continue using this tool in harmony with its nature.