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: 
potter of 28 years experience here. What you are seeing is called crazing. It's caused by a slightly poor "fit" between glaze and clay body of the ceramics, usually because of too much silica in the glaze. With some glazes, it's intentional; [celedons craze](https://digitalfire.com/glossary/celadon+glaze), as do [white raku](https://ceramicartsnetwork.org/daily/ceramic-glaze-recipes/low-fire-glaze-recipes/fergusons-white-crackle-raku-glaze-recipe/) glazes.

What you're seeing there is unintentional crazing. It's fairly common for this to appear at the first time you use it with a hot liquid, or microwave it. What's happened is that the glaze is 1% smaller than the clay body, so the first time it heats and cools, it crackles.

Whether or not eating off of crazed glazes is a health hazard is [a matter of some debate](https://digitalfire.com/article/crazing+and+bacteria%3A+is+there+a+hazard%3F). It's prohibited for most restaurants in countries with strong sanitary regulations, although rarely enforced. For home use, I personally wouldn't worry about it; you pick up more bacteria off your kitchen counter than you will from the cracks. There's one exception to this though: if the dish is low-fire earthenware, or made from a clay that was not [fully vitrified](https://stoneleafpottery.com/vitrification-nation/2014/08/19/), then the cracks can allow the underlying clay to absorb liquid. In addition to being a bacteria hazard, such absorbed liquid could cause (for example) the dish to explode in the microwave.
It is safe to use. I have seen lots of cups with similar cracks. I think that they are only in the glaze, not in the ceramic below. But even if the ceramic is slightly damaged too, I have never had one of these break in my hands despite using them for years.