Seal a hairline crack in a ceramic cup

June 13, 2013 3:17 PM

I dropped my handmade ceramic cup which was a one of a kind gift and now there is a 3-4 inch long crack that appears on both the inside and outside of the cup. Is there a safe way to seal the crack so I can continue to drink from it (sans poisoning), and that will keep that crack from extending so that cup doesn't fall apart?
posted by boygeorge to Home & Garden (13 answers total)

Cyanoacrylate glue (of which Krazy Glue is one brand) is also used to close up cuts after surgery, so it's got to be relatively human safe. There are very liquid versions which are pretty good for soaking into cracks (I use 'em for crack filling in woodworking).
posted by straw at 4:32 PM on June 13, 2013 [1 favorite]

The last time I had this happen to me, I repurposed the mug as a pencil holder. If you can't repair it in a watertight way, you might still get some use out of it that way..
posted by Johnny Assay at 4:43 PM on June 13, 2013

Oh, if it's ceramic, can you put another clear coat of glaze over it and have it fired again? Local ceramics studio should do this easily...
posted by straw at 4:47 PM on June 13, 2013

Agreed, Krazy glue is perfect for this application. My mom used it for ceramic cups and plates that were badly cracked and even split in half. She used to put the glue on cracks and even fill in holes - often used ducttape or electrical tape to hold the piece together while the glue dried. No one got sick from it at my house , even when used in the microwave.
posted by NorthernAutumn at 5:39 PM on June 13, 2013

Kintsugi?
posted by fings at 5:45 PM on June 13, 2013 [2 favorites]

Unless you have some specific information about the initial glaze firing conditions of your cup, I would be hesitant to refire it b/c your glazes could react and change significantly. Sometimes reglazing and refiring can make cracks worse. Also if you have a piece that is soda/wood fired, whoever's firing it has to prop it up etc for the refire so it's not always straightforward.

I looked into some of the kintsugi diy kits but haven't tried them, and I would be interested if anyone has any actual experience with it.
posted by tangaroo at 5:58 PM on June 13, 2013

Have you checked to see if it's still watertight? My father's favorite teacup had this happen and it doesn't leak and he's used it to drink tea for many years after the initial crack. The crack hasn't become longer, either.
posted by quince at 6:27 PM on June 13, 2013

If you use CA glue, make sure to select a "penetrating" low-viscosity variety that will seep nicely into your crack, rather than the "gap-filling" high-viscosity variety. For example, if using Loctite, get Loctite 420.
posted by Behemoth at 6:51 PM on June 13, 2013 [1 favorite]

Cracked china cups used to be repaired by boiling them in milk. Googling that idea brings instructions to put the cup into a large vessel, carefully, then slowly pour milk over the top of the cup until it's submerged. Heat the milk slowly to a boil, then turn down the heat and simmer for about an hour. Let cool completely before you remove the cup. I don't know if this will work or not, but I know my grandmother fixed more than one piece of cracked china by boiling it in milk.
posted by aryma at 7:36 PM on June 13, 2013 [1 favorite]

Sugru. If you look on their website, you can see how other people fix their cups.
posted by QueenHawkeye at 7:48 PM on June 13, 2013

Best answer:

fings: Kintsugi?

To take this further...

It's almost impossible to keep this crack from spreading further. Instead, go with the flow. Put the cup in a sinkful of water, and finish breaking it into two pieces - the water will reduce the surface tension difference and diminish the odds of shattering.

Dry thoroughly, and reglue the pieces with epoxy. I'd pick J.B. Weld 2-part epoxy over cyanoacrylate, but superglue can work well too. Cyanoacrylate wants a molecules-thick layer of water to finish bonding; either breathe on one side, or rub with a barely-damp cloth, then glue and press together for 5 minutes. If you go with J. B. Weld, you'll need to clamp overnight; while I think it's more durable by far, it dries to a dark grey.

Kintsugi technically requires mixing powdered gold with resin; I've always wanted to do it with JBWeld and gold foil, pressing the foil on after an hour or so when the glue is very tacky.
posted by IAmBroom at 7:28 PM on June 16, 2013

straw: Oh, if it's ceramic, can you put another clear coat of glaze over it and have it fired again? Local ceramics studio should do this easily...

This won't work. The stresses of heating will spread the crack; if they didn't, the uneven contraction of the glaze would.
posted by IAmBroom at 7:29 PM on June 16, 2013

So there is actually a kit to do the kintsugi thing at home which I am going to try.
posted by shothotbot at 5:41 PM on April 21, 2014 [1 favorite]