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My glazed ceramic teapot has exhibited hairline cracks since I thrifted it. Tiny droplets of tea tend to bleed through, which probably means it isn’t foodsafe.

After a small shock to the pot’s exterior, two long thin shards have fallen out, leaving a larger cavity (image below).

I’m wondering what I can do to render this teapot usable, foodsafe, and leakproof. Is there a coating I can apply to the inside to prevent water from contacting the cracks and to prevent further damage?

Image of crack in side of teapot

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  • There’s a Japanese technique called kintsugi ( en.wikipedia.org/wiki/Kintsugi ) that I think is used for pottery still being used (including food vessels), but I don’t know if it works for cracks or if it needs to be separate pieces to be joined back together
    – Joe
    Oct 8, 2023 at 19:29
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    Given the precautions I see around lacquerware (which is made with the same sort of lacquer used for traditional kintsugi) and boiling water, I have my doubts as to repairing a teapot with it. The lacquer should be safe when cured. These days one also has to beware of lookalike techniques that use materials less likely to be foodsafe than the traditional lacquer and gold dust.
    – Ecnerwal
    Oct 8, 2023 at 19:43
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    I would suggest that while you could try a repair that would be food-safe you can't repair it in a way that is actually safe as that pot looks like it will come apart on you, spilling boiling water all over.
    – GdD
    Oct 9, 2023 at 11:53
  • Why would droplets bleeding through mean it wasn't food-safe? Either way how could any permanent, insoluble seal not be food-safe? Superglue can't qualify because it is moisture-soluble… Instead, read FuzzyChef, below. Oct 9, 2023 at 19:31

6 Answers 6

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Potter here. Those cracks are very bad, and are the kind that will continue to spread each time the teapot heats and cools; I doubt you have too many uses before it falls apart entirely. You should consider whether it's worth trying to salvage that teapot at all. Assuming you want to, though, I'll outline the methods.

Those cracks, by themselves, are not a food safety issue. Tea is fairly antiseptic, and just having some in the cracks doesn't really expose you to anything. It's pretty common to make teapots out of porous earthenware because nobody is worried about bacteria in tea.

You have three ways to seal those cracks: epoxy, silicone, and milk.

Epoxy: various food-safe epoxies can be used to fill in the broken areas. This will make your strongest and most durable bond, and will fill that divot nicely. However, it's going to be difficult to seal the hairline cracks, because there's no way to get the epoxy into the crack. You could consider cracking the teapot the rest of the way, and then epoxying the whole thing back together. Some people even do this with decorative elements in a technique known as kintsugi.

Silicone: there are also various food-safe silicone sealants. While these do not have as much binding strength as epoxy, they will fill that divot well, and possibly work better for smearing on the hairline cracks to seal them. You can also use a dilute silicone sealant to try to coat the inside of the pot. However, such sealants don't bind well to glazed surfaces, and may affect the flavor of the tea.

Milk: the casein in cow's milk has been used as a sealant for earthenware pottery, and for crazed glazes. While this won't bind the crack (you'll still need epoxy for that), it's obviously a cheap and easy way to seal the inside. However, the sealing ability of milk is disputed, and the milk technique is not generally used for vessels that will hold hot liquids.

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    Re: "Food safety isn't really relevant here. Tea is fairly antiseptic, [...] nobody is worried about bacteria in tea": I think this is a bit too blanket a statement. (1) People do sometimes get sick from bacteria in tea, usually because the tea was heated for a long time at low heat (e.g., outside in the hot sun) instead of a short time at high heat. (2) The term "tea" sometimes includes herbal teas, which don't all have antiseptic properties. (3) There's more to food safety than just bacteria; obviously it wouldn't be safe to seal the crack with a material that leached toxins into the tea!
    – ruakh
    Oct 9, 2023 at 5:01
  • @ruakh for example... if heat melted the sealant, and then you drink it, that's not going to be great for you. Something like low-heat glue gun would be quite bad, not to mention your pot falling apart anyways.
    – Nelson
    Oct 9, 2023 at 7:28
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    @AravindhKrishnamoorthy - Filling an expansion crack with something that has an even higher coefficient of expansion seems somewhat counter-productive. It would aid the breakage rather than prevent it. Adhesion is likely to be a problem too.
    – Tetsujin
    Oct 9, 2023 at 15:02
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    I've edited my statement on food safety based on the comments.
    – FuzzyChef
    Oct 9, 2023 at 15:24
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    @AravindhKrishnamoorthy Molten metal will not bond to ceramic, by itself. The "gold-filled cracks" you've seen for things like Kintsugi are a mixture of gold powder and epoxy.
    – FuzzyChef
    Oct 9, 2023 at 15:25
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There really isn't a foodsafe practical repair method.

If you had a pottery kiln you could attempt re-firing it, but if you had a kiln your time would be better spent making a new teapot and letting this one go on to future archeologists. And letting this one go on to future archeologists is definitely the practical, economical and food-safe approach without a kiln.

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    You can't re-fire a piece of pottery to seal cracks. It doesn't work that way. Cracks just get worse with each firing.
    – FuzzyChef
    Oct 8, 2023 at 20:07
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    I've known people to pull off remelting glaze and cover/seal a body crack, but failure is more likely than success, to be sure, and I do feel (and stated in the answer) making a new one would be a better way to spend the time, effort and kiln fuel.
    – Ecnerwal
    Oct 8, 2023 at 20:24
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    Kaddath: I'm afraid that's not accurate. For mid-fire pottery, glaze firing temperatures are generally 250C hotter than bisque firing, and for high-fire, they are 400C hotter. Even for earthenware, the glaze firing temperature is the same as the bisque temperature. The only time you glaze fire pieces at a lower temperature is for lusters, like gold rims.
    – FuzzyChef
    Oct 11, 2023 at 21:21
  • FuzzyChef maybe I get old and my memory gets bad :D The person I used to talk about this only worked with ceramic (>1000°c) and composed his own glazing formulas from chemicals, maybe he had his own ways
    – Kaddath
    Oct 12, 2023 at 7:39
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Take it to a dentist and have them fill the crack with tooth repair epoxy, the kind that's UV cured. A good dentist can even match most off-white colors, the repair should be invisible. I don't know how thermally stabile it will be, but it sure will be food safe, if the stuff can stay in your mouth for years.

Of course, the cost will be much more that the cost of a new pot.

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Foodsafe isn't the issue. Burn-safe is.

Cracks in ceramic tend to spread, first slowly and almost invisibly, then catastrophically. There's a stress concentration at the tip of the crack, which you can't get glue into. Every time the pottery changes temperature, it expands or contracts, and that will tend to advance the tip of the crack.

One day, the pot will disintegrate while you are carrying it or pouring from it, and you may get scalded. Possibly very seriously.

A repair might be acceptable for a container of cold drinks, or even warm drinks. But a teapot full of almost-boiling water? I would strongly suggest its had its day. Buy a new teapot, and throw this one away, or keep it as a non-functional ornament if that's why you want to fix it.

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I'm not a potter though I've fixed ceramics using epoxy resin before, and I'm facing a similar situation with a couple of pieces with cracks of varying sizes.

I'd love to get comments on this idea: you could coat the entirety of the inside of the pot with epoxy, and then use whatever glue works best on the cracks (e.g. runny superglue on hairline cracks, or more epoxy on the bigger ones). The epoxy 'lining' will be leak-proof, with the drawback of there being a lot of epoxy in contact with the liquid if that's a concern.

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    Don’t use superglue. Most of them are CA (cyanoacrylate), a cyanide substance that is NOT good safe. I think that one of the ‘krazyglue’ formulas doesn’t use cyanide, but I don’t know if it’s necessarily food safe. (Some may be good safe for occasional contact for a kid but not prolonged contact, or for acids, etc)
    – Joe
    Oct 11, 2023 at 17:22
  • The only coating epoxies I could find were meant for flooring and were definitely not OK with food. That's why I didn't mention it as a possibility; I don't think such an epoxy is commercially made.
    – FuzzyChef
    Oct 11, 2023 at 21:29
  • @FuzzyChef, there are food-safe coating epoxies, commonly used to make 3D prints food-safe.
    – Mark
    Oct 12, 2023 at 1:03
  • @Mark link? Like I said, that's the reason I didn't include that as an option in my answer is that I couldn't find any products.
    – FuzzyChef
    Oct 12, 2023 at 17:51
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Just a suggestion: Stalactites and stalacmites.

stalactite water evaporates and fills microcracks with limestone.

You can search for someone online who has made artificial stalactites by dripping water through cement, and copy their process.

Perhaps it will take a few months depending on temperature, but a drip drip of stalactite water into the cracks will should seal it as well as a stalactite is glued to a ceiling. perhaps research stalactite hardness chemistry too lol.

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