microwave proof?

[dondon]

Hi, What is the correct temperature to fire at to make pots ovenproof and microwave proof.

thank you, any advice appreciated.

Don

[Chilly]

There are many answers to this question, which is probably why no-one else has answered you yet.

So, here's my take on this:

First the clay and glaze must fit each other, and must be fired to maturity.  The actual temperature is relevant to the clay and glaze used.

Second the glaze must not leach unwanted chemicals into the food or drink.

Third, after you've sorted points 1 and 2, you need to get your pots tested by a commercial agency if you're going to sell them.

Finally, you need to ensure you can make, glaze and fire your pots consistently thereafter.

Search the forums for more answers, this question has been asked many, many times.

[Joseph Fireborn]

I think the definitions for what your calling "oven proof" and "microwave proof"are probably important towards people answering this question. In reality nothing is "proof". If your using proof as part of your marketing language I would change it to "safe", which infers a sense of "intelligence required".  For example, cars are safe, but people die in them every day. No car manufacturer would say this car is driving/wreck proof! because they would probably get sued the first time someone died in it. 

Just some thoughts. 

As far as your questions:

In general, microwave safe is considered low absorption pottery. Meaning that if the pot isn't going to absorb enough water that when put into the microwave heats up the actual walls of the piece. If it does heat up, it means the pot is holding too much water and probably has a high absorption rating in the 3-4%+ range. Ideally if your making pottery that is to go in the microwave you want to use clay that when fired to maturity has an absorption rating of <1%. 

Oven safety is a completely different monster. You can have a perfectly fired strong industry made dish break in the oven because of ignorance. For example I just cracked a dish the other day because I was in a hurry and I wasn't thinking.  I took a dish from my cold refrigerator and slapped it into a 425 degree oven. The dish didn't break in the oven but when I took it out of the dish washer I noticed a large crack down the entire thing. Woopsy. This was a well made dish from a reputable company as well. So there is no such thing in my opinion as "oven proof". Even if there was a really well made dish that touts oven proof, if you repeatedly shocked it the way I did. I bet it would crack just the same. I would say that any dish that passes the microwave safe test, also should be considered oven safe when used properly.

Hope this helps. Good luck.

 

[glazenerd]

Relative to this topic: a niche where clay becomes as important as glaze or firing. Oven ware, flame ware, or by application: microwave "proof." Every time you heat a pot, rather by heat or microwave, you are dealing with expansion and contraction. It is one thing for a coffee mug to get a quick shock of heat, and another for a piece to be subjected to increasing amounts of heat over an extended period of time.

what Chilly and Joseph added is relative: but in this case so is the clay. Ovenware, flame ware clay bodies are low expansion: 4.25 up to 4.75 median average. The lower expansion of the clay, the more resistant to shock it becomes. Wall thickness also comes into play: the more clay present equals more clay that expands.  The lower COE clay also means extensive adjustments in COE in the glaze of choice to fit it.  Spodumene will quickly become your friend, should you venture down this road. I will let others work the glaze side of this equation, being a clay guy primarily.

nerd

[Mark C.]

Another issue for microwave is iron. If your clay body contains iron that will heat up the pot and if its a rich iron bearing clay it can damage the microwave . The usual effect its a very hot pot with typical stone wares bodies.My Porcelain clay body since its iron free microwaves well.