Why are my ceramic baking dishes cracking?
Over the past five years I've accumulated a nice collection of ceramic baking dishes, some of them from Spain and Portugal, a few from Ross (but with reputable labels like Cuisinart).
There's no indication that any of them are cheap knockoffs or anything like that, so I trust that they can be used as designed: to bake or roast everything from whole fish, to apple crumbles, to casseroles.
Here's the weird thing: one by one, they've started to crack. First a slight crack shows up in the glaze on the inside (or enamel, for those that are painted rather than just glazed terra cotta), then the crack shows up on the bottom. One actually cracked in two with a whole fish in it, in the oven, in the middle of the cooking time.
Does anyone know why this is happening? It's been in two different ovens (in two different countries, no less!) -- one gas, one electric. I've never dropped any of these dishes, or put them in the dishwasher, or subjected them to sudden shifts in temperature (other than putting them into a preheated oven). No freezer to oven, or oven to cold water, or anything like that.
What is causing it and what can I do to avoid it happening in the future?
ETA I did see this old post on the topic, but no one seems to have an answer. I'm not so worried about superficial cracks in the glaze - it's the cracking all the way through while cooking (or visible cracking on both inside and out in the exact same spot) that has me worried.
Are these glazed both inside and out, or just inside?
I have a Spanish cazuela, glazed on the inside only. As per instructions I soaked it after purchase. I use gentle gas flame, or start it in a cold oven. I don't know if it would handle a preheated oven or not. So far no breakage, but I don't expect it to last for ever. Same goes for an inexpensive Chinese sandpot.
It's not cookware, but I have a set of ceramic dishes (place settings) that have lasted for 12 years with not one chip, scratch, or break, with two exceptions...both times, I was heating something greasy in the microwave, and the small plates cracked in half. So this makes me wonder if maybe your dishes are cracking due to overheated oil or grease???
(Seriously, I WISH these dishes would break so I could justify buying a new set! They seem to be invincible!)
Any piece which contains even a microscopic crack will eventually crack under temperature changes, because the stress in the material is concentrated at the end of the crack. It isn't necessary to have a large thermal shock for this happen. So a material and manufacturing process which minimizes the possibility of cracks being present at the time of manufacture will result in products more resistant to cracking.
I don't have it yet, but I am planning to get a Pillivuyt porcelain baking dish soon. It seems to me that their pressure forming process should address this problem. It would take awhile to find out, however.