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.
Cracks in any dishes hold bacteria so they are always unsafe. Never use dishes with any cracks in them for food. Chips on edges of plates or serving dishes do not really present a problem, but all tiny cracks present a health problem and the poster is also exactly right about leaching into the cracks and molds and staining resulting. If dishes have any cracks, even tiny crazing, you should think of them as unsafe for foods and eating, any kind of foods, even dry foods. And what is unsafe for humans is also unsafe for your pets. Bacteria that you do not know about can be deadly. That is why it is important for human animals and pet animals to eat cooked foods.