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Stephen

Oven Safe

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Ya know I know this has been covered but I keep coming up blank. Would never make anything that would come into contact with flames with porcelain but wanted to add pie and quiche dishes to my booth for holidays and can find surprising little in my searches on if this is ok, here and elsewhere. I do know that porcelain from a refrige straight to hot oven might/would crack but but most people know that, right?

 

I do see them at various potteries but they may just be clueless like me :-)

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Stephen, I am with you on the confusion.  I know lots of potters who make casseroles and pieplates. Many tutorials have been created on how to do make those items.  But when I emailed Laguna and Aardvark, they said their clay is not designed to go in the oven.  That response could be a CYA response.  I tend to err on the side of caution, so I just have not make items that go in the oven.  One clay guy told me he puts something in his clay to make it oven worthy.  Ground up pyrex, maybe? 

 

Roberta

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My mentors used to do a lot of baking dishes out of 2 different clays over the years: Plainsman's p600, and B-mix. They fire to cone ten, and they glaze test very thoroughly for glaze fit and all kinds of food safety. You need a *very* even cross section on the pots to prevent thermal shock, and the baking dishes have to be put in a cold oven, and then brought up to temperature.

Despite warning people extensively, there are always one or two people who come back and complain that the pots had cracked in use, and every time it was because they put a cold dish in a hot oven. The number of people that do this isn't that high, so they just offer good customer service, and either discount the next one if the customer is mean, or replace if the customer is nice.

 

They're getting closer to retirement, and they're making fewer of the pots they don't like to make anymore, and that includes the baking dishes.

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I make and sell pie plates from Daves Porcelain.

I used to make casseroles but the market has tanked on them so no more.

The pies need to go into a cold oven and warmed up evenly. I use one at home and always throw it into a hot oven so I know its works.

These pots are fired to a soft cone 11 in reduction.

I have sold pie plates for over 40 years-I have replaced less than 4 but it always some idiot who puts a cold one in a hot oven.

Pies sell well in the fall-I make about 50  or more a year.

You will need to test your clay and glazes to see if they can handle the heat.

I have found tighter bodies do dot work as well and fail more easily.I also make larger baking dishes and use 1/2 and 1/2 from Laguna the kind with grog in it. These are shaped like a pyrex baking dish-a large rectangle made from Daves and WSO which is the 1/2 and 1/2-I also make a smaller one.

You need to test them as well in your oven

 

A flame proof body is another animal altogether.

 

Your pots are all fired in an oven of shorts called a kiln-they get hot and then cool off the question is can they do this again with food in them.

A few tests and you will know.

I test them hard so I know what they can take.

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I honestly have no idea how our class can have over 30 different glazes, 8 different clays, and not once using any combo of these have I had a pot crack or break being put in a dishwasher, oven, or microwave. And I can be quite ditsy! I have used everything from porcelain to red clays with any assortment of glazes, thrown them in the oven (that was hot) and microwaved them without the slightest hint of crazing, cracking, or breaking.

 

I have no idea what my professor does to prevent tragedies from happening with so many newbie works. Only time my stuff breaks is when I drop them :blink: 

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There is always going to be somebody who puts a cold pot in a hot oven or a hot pot in a sink of water. Doesn’t matter what instructions you give with the pot warning not to do this.  I think this comes down to how comfortable you are dealing with an unhappy customer(s) at some point in time. 


 


Low COE clay with a well fitting glaze, rounded pot base, even thickness of base and walls, no sharp corners where base meets walls, even drying to avoid building up stress are all going to help. At some point in time if you sell a lot of ovenware it is inevitable you will have to deal with an unhappy customer who has abused the pot and it’s cracked.

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I will echo what others have said above, the only way to know if YOUR pots are oven safe is to use them yourself. And that ovenware needs a very even cross-section, and have generally thicker walls than an average bowl or cup. My only story of oven failure happened when a customer put the pot under the brolier, very close to the element. Now when I sell oven pieces, I tell them to keep it in the middle of the oven, not close to the bottom or top elements.

 

I also agree with Mark that casserole sales are down, but pie plates still sell great.

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I use home-made casserole dishes in the oven, some of them have been reduction fired to ^10 and some electric fired to ^6.

 

I've never had a problem, not even with cool, (not cold, just room temperature) dishes going in the oven.

 

I'd have to say, I've never given it a moments thought before, the oven goes up to about 230°C (140°C -150°C max. for a casserole) and the kiln has already taken them past 1200°C.

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Several customers asked me at last weekends art show how hot can these pie plates go to-My answer is always the same 2,400 degrees and try to keep the fire dept from spraying water on the house fire when it gets up to that temp as the water will cool the pot unevenly.

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Cristobalite inversion can come into play with some clay bodies used in an oven over about 225C (approx 440F). Well within the temp home ovens get to. How long does it take to get through that temp for refired work in the kiln  or cool down from that temp to room temp, compare that to how long it takes an oven to get to it. Big difference in time the kiln takes versus oven. Sounds like a clay body for Nerd to perfect  :rolleyes: 


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But when I emailed Laguna and Aardvark, they said their clay is not designed to go in the oven.

Which means there are ways to formulate porcelain to increase its thermal shock capacity.

---Wedging in as little as 5% Missouri grog (calcined flint clay) will help considerably.

 

The better way is to switch out 1/2 the silica for pyrophyllte, and throw in some grog for good measure. However, you are talking about formulating a porcelain body from scratch. The amount of alumina in the body and the glaze also plays a role. ---but serious testing is still required to ensure results.

 

Nerd

 

 

Sounds like a clay body for Nerd to perfect  :rolleyes:

Already have.

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Sounds right to me. We have always had first dibs on any ware with slight imperfections for our home dishes and that has always made me feel great about our wares as we use them day in and day out. We also don't coddle them at all want to really step them through the paces so if anything we use them to reckless abandon.

 

Sounds like I am going to have to take one for my customers and eat a lot of pie and quiche between now and my first show after thanksgiving :P

 

Hey Nerd you may have given me a reason to justify keeping my two grand blue bird mixer I bought 5-6 years ago now and never use. 

 

Thanks everyone! 

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Several customers asked me at last weekends art show how hot can these pie plates go to-My answer is always the same 2,400 degrees and try to keep the fire dept from spraying water on the house fire when it gets up to that temp as the water will cool the pot unevenly.

 

 

I love this response Mark!  Do you get blank, startled stares when you say it, or do the customers get the joke immediately?

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I have Aardvark porcelain (Nara 5) and Laguna Speckled Buff and Laguna SB Red.  The two Laguna clays are groggier.  If I understand what everyone is saying, Those two clays would be better for pie plates??

 

Roberta

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Several customers asked me at last weekends art show how hot can these pie plates go to-My answer is always the same 2,400 degrees and try to keep the fire dept from spraying water on the house fire when it gets up to that temp as the water will cool the pot unevenly.

 

 

I love this response Mark!  Do you get blank, startled stares when you say it, or do the customers get the joke immediately?

 

Most laugh -I have said this for decades

I have been told I;m hard on some customers.

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Several customers asked me at last weekends art show how hot can these pie plates go to-My answer is always the same 2,400 degrees and try to keep the fire dept from spraying water on the house fire when it gets up to that temp as the water will cool the pot unevenly.

 

 

I love this response Mark!  Do you get blank, startled stares when you say it, or do the customers get the joke immediately?

 

Most laugh -I have said this for decades

I have been told I;m hard on some customers.

 

As someone, who has worked shows for the amount of time you have, I'm sure your demeanor is appropriate.  Plus, your work speaks for itself.  Customers can buy smiles and sunshine from another artist.  Talk to you if they want quality wares.

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