My teapot lining flaked
June 7, 2020 3:26 PM   Subscribe

I have a tetsubin that I got in 2006 that is cast iron with some kind of inner lining. Today some dark flakes came out of the spout when I was cleaning it with a bottle brush. They were between an eighth and a quarter of a square inch each. Can I still use it?

My tea was lemon balm which is green leaves, so it wasn't the leaves themselves. I only use it for tea, so it holds boiling water and the leaves stay in the removable strainer. I scrubbed the area more and did not see any additional flakes. I can't get a good picture of the inside of the spout. The white stuff you see inside the pot comes off when wipe it, so probably just from the water.
posted by soelo to Food & Drink (5 answers total) 1 user marked this as a favorite
This, from Wikipedia, might be relevant:

"Outside Japan, a frequently seen variant is a cast-iron teapot that outwardly resembles a tetsubin. This type of teapot is glazed with enamel on the inside to make it more practical for tea brewing, though it can't be used to heat water because that would break the enamel coating."
posted by pipeski at 3:34 PM on June 7, 2020

... so it might be that the boiling water is too hot.
posted by pipeski at 3:35 PM on June 7, 2020

It's enamel flaking off. Can still use it, absolutely -- just now there's exposed iron inside (which is nbd).
posted by so fucking future at 6:36 PM on June 7, 2020

On the other hand, if it's real tetsubin... Well Iron rusts, but it rusts in at least two different ways. One is the red rust that everybody knows about. The other is black and still oxidation (rust) but occurs under high temperature and the right oxygen levels. Strangely enough, the second black type once formed protects from the first red type. In a real tetsubin, those black flakes would be that protective layer of 'good' rust that chipped off. Depending on how deep the layer of oxidation is the pot may still be fine, if only a bit of the protective layer cracked off and there's more left under it. If it flaked off down to the raw Iron, then that little spot is now prone to do the red rust thing if left wet. Strangely enough the thicker the black protective layer is, the more likely it is to eventually crack due to thermal expansion differences between the raw Iron and the black rust layer. The really good tetsubin have a really thin layer of the protective rust that lasts longer.

Why yes I have watched a NHK program on tetsubin manufacturing.
posted by zengargoyle at 6:39 PM on June 7, 2020 [4 favorites]

Response by poster: I don't heat the water inside the tetsubin, by the way. I heat it in an electric kettle and pour it in for steeping. I have no fear of bare iron and I will keep an eye out for red rust and any more flakes.
posted by soelo at 9:17 PM on June 7, 2020

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