Question: I have a large ceramic soup cup which appears to be internally damaged after being rinsed with cold water while hot:

![Ceramic cup with visible cracks throughout](https://i.stack.imgur.com/kj0v8.jpg)

Is this cup still safe to use, or is it likely to shatter or otherwise fail during use?

Answer: 
That is called crazing. It is a crack or fissure in the enamel coating on the cup, not indicative of deep structural flaws.

Your cup is unlikely to fail in the sense of completely breaking due to the craze in the glaze.

On the other hand, they will stain over time, and be unsightly, and hard to wash out. 

If the piece is old enough, the glaze may contain lead, which can leach due to the crazing. In that case, the piece should definitely be discarded.

Technically, most health codes require crazed dishware to be discarded, although you can assess your tolerance for risk.
Looks [crazed](https://www.google.com/search?q=crazed%20ceramic&safe=off&client=firefox-a&hs=2QS&rls=org.mozilla%3aen-US%3aofficial&tbm=isch&tbo=u&source=univ&sa=X&ei=7fXBUo6bAo7AkQeW1oCACQ&ved=0CE4QsAQ&biw=1478&bih=783). Sometimes that's a death sentence for a cup, more often it means that dark colored liquids can seep into the cracks, and make things look interesting. Sometimes not even that happens, and you just have a cup with an interesting pattern in the glaze.