Glazed clay casseroles

[seabream]

I have a glazed clay casserole, and have the following questions about its care:

1. Can I place the casserole directly in a hot oven? Or do I need to place it in a cold oven and then turn it on, like is recommended for unglazed casseroles?

2. Can I place a room-temperature casserole under the broiler? Or should I place it in the cold oven when I turn on the broiler? Or should I simply not use it under the broiler?

Any comments are very appreciated!

[haresfur]

The answer is that it depends on the clay.(and the glaze). Because of the different thermal properties between the clay and glaze it could be more subject to thermal shock. If it is not specifically formulated for it, I would not use it under the broiler. As far as the first question goes, it would be safer to put it in a cold over, I usually put mine in a hot over, but it's a gamble.

[Panaderia Canadiense]

And here's a completely different perspective: in Latin America, if it's got glaze on the inside it's a glorified tureen. You cook in some other vessel and then transfer that food into a warmed glazed clay pot (warm by filling with hot water, then draining just before transferring the food). This prevents any nastiness from the glaze (which is often leaded) into the food during the crazing which is inevitable when you heat these pots.

[rancho_gordo]

I don't know. I've seen lots of Mexican chefs cook in glazed clay ollas, cazuelas and even comales.

I prefer the unglazed, that's for sure.

But in any case, i've only seen them use them on an open flame, on a stovetop or some kind of barbecue set up. Not in the oven.

[Raoul Duke]

I'm currently using a variety of sizes of un-leaded, glazed La Tienda cazuellas in a standard oven and, principally in a wood fired oven at temps from 200 to 700 degrees. In the wood oven I introduce them slowly, rotating often without issue. For specific dishes I preheat the clay prior to using them in the wfo.

[haresfur]

So, if anyone is interested in more detail, a well formulated glaze will put the clay under a little compression. This will make the pot stronger. If the glaze shrinks a lot more than the clay upon cooling, it will craze - i.e. get cracks in the glaze. Crazing can cause 2 main problems in cooking ware. First, for an earthenware clay the clay is still very porous after firing. Liquid can get into the clay and when it turns to steam it can further damage the glaze or because it is trapped to some degree under the glaze break the pot. Stoneware is fired to a high enough temperature that you won't get water absorption. The second problem is that you can get food seeping into the cracks and that could harbour bacteria. Personally I don't think that's a great problem but some people worry about it.

So there is a big difference if you are talking about earthenware like they use mostly in central/south america and the middle east or stoneware. I do own high-fire stoneware au gratin dishes that have survived some broiler use (I think - not my usual cooking). I haven't heard of older stoneware building up stress over time then failing spectacularly like, say, pyrex.

And stay away from the lead glazes. Even though a well designed one won't leach much, it's impossible to know without testing and besides it usually isn't healthy for the potters.

[Smithy]

Thanks for that explanation about the glaze and crazing, haresefur. I have to admit that I'd only thought about glaze in terms of porosity and lead content; I hadn't thought about the glaze acting as a moisture trap for the internal pottery. Furthermore, I had no idea that crazing was due to a difference between the thermal expansion coefficients of the glaze and the underlying clay. Fascinating!

[seabream]

Fantastic replies everyone! haresfur - that really was a great explanation. Thanks for teaching us something.

[Paul Bacino]

_{We've had a Romertopf clay cooker for yrs. I usually soak it first, it has a glazed bottom..both top and bottom and put then put it in the oven cold, Come to think of it I may even put it in a hot oven.. never had a broblem,,}