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Developing A Cookware Clay Body

cookware fireclay developing clay body fire direct

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#1 lbrown1020

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Posted 01 May 2014 - 10:31 PM

Hello!

 

I am new to the forums and I am very new to ceramics and the more technical side like developing glazes, clay bodies, ect.

 

That said, I am interested in cookware. I want to find a formula for a clay body that will be able to withstand repeated use at high temperatures, as well as being used over direct flame and heat.

 

If I am posting this in the wrong category please forgive me.

 

Any information at all is helpful because at the moment I have none.

 

Thanks!



#2 Mark C.

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Posted 02 May 2014 - 01:16 AM

Use the search window at the top right while viewing all forums and type in flameproof

there you will find this discussion on at least 4 threads.

This clay body will be expensive to make-just a heads up on that.

Mark


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#3 Marcia Selsor

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Posted 02 May 2014 - 07:34 AM

Are you developing a flameproof body?
Flameware's most difficult challenge is getting glazes to fit.
Do lots of research. It is technical. Maybe search in the American Ceramics Society Engineering Division.

Marcia

#4 neilestrick

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Posted 02 May 2014 - 09:13 AM

Flameware bodies often have spodumene/lithium in them, which reduces their shrinkage rates considerably. I used to use one that had close to zero shrinkage from wet to done. This causes most glazes to shiver off. So you'll have to find/develop some low shrinkage glazes to work on them.

 

From a liability standpoint, I personally don't have the guts to sell flameware pots. I think the risk of damage and injury is too great. Call me paranoid, but I think at some point a pot is going to give out on a stove top and make a big hot mess. That said, there are people who sell flameware. I'd like to see what their insurance company thinks about it, assuming the insurance company even knows the potential dangers.


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#5 Venicemud

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Posted 02 May 2014 - 09:18 AM

If you want to develop your own flameproof clay body  don't read any further, but if you want to buy one you might consider mica clay.  I have bought the red mica clay from New Mexico clay company and made cookware that was used over an open flame and on an electric stove - also in the oven.  The ware is not glazed and does stain with use, but can be refired(I suppose - never did it) to burn out organics.  It was a fun clay to use but if you are selling cookware I'd listen to Neil. Joan.



#6 JBaymore

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Posted 02 May 2014 - 09:32 AM

From a liability standpoint, I personally don't have the guts to sell flameware pots. I think the risk of damage and injury is too great. Call me paranoid, but I think at some point a pot is going to give out on a stove top and make a big hot mess. That said, there are people who sell flameware. I'd like to see what their insurance company thinks about it, assuming the insurance company even knows the potential dangers.

 

Add me to this category.  If you make flameware (the usual name for this stuff) you likely should 1.) spend a bunch of time researching the technical side  2.) consult a lawyer  3.) form a L.L.C.  4.) get good product liability insurance

 

Personally...... I'd never touch the stuff.

 

And functionally on a stovetop.... such material does not have a high termal conductivity when compared to metals.  So right over the flame, the cooking surface gets way hotter than the surrounding areas.  Pain to cook with.  More a "novelty" idea in my book.

 

best,

 

.....................john


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#7 Tyler Miller

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Posted 02 May 2014 - 10:07 AM

It should be added that the reason for all the legal liability stuff is that some glass and ceramic flameware has a nasty tendency to shatter explosively when it does crack.  This is because they don't release stresses like normal ceramic does.  They kindof "store" it up.  Eventually you get a pot that all you need to do is bump the wrong way while washing and you've got a trip to the emergency room on your hands.

 

Low fired earthenware makes a nice, safe, cookware for personal use, though.  Micaceous clay is a great example of that, as Joan mentioned.  No better way to cook beans or rice. :)



#8 neilestrick

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Posted 02 May 2014 - 12:01 PM

I guess I'm not so paranoid after all! For oven use, a good stoneware will work fine, just don't preheat the oven and don't go from freezer to oven. Even if they do crack, they just crack, not explode, and the mess is contained within the oven if it leaks. But I've actually never seen one leak when it cracks. Usually you notice the crack later when cleaning up.


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#9 Tyler Miller

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Posted 12 May 2014 - 09:57 PM

I've done a little more research into the exploding flameware phenomenon, and it's not quite the issue I made it out to be.  The issue really comes into play in modern, commercially produced flameware bodies of the prestressed variety.  Visions cookware and the recent formula change to lime-soda glass Pyrex made are the two most notorious examples.

 

Glass and vitreous ceramic flameware can either be low-expansion or pre-stressed.  Low expansion bodies are the ones mentioned in the above posts, lithium and borosilicate bodies.  As far as I know, they don't explode.  Prestressed flamewares are formulated so that the bodies are under tension constantly.  I was incorrect that they build up and store stresses.  They're there from the beginning.  They get their strength from the fact that they're already under tension.  Imagine pulling a rubber band taut and then someone else trying to stretch it in the axis perpendicular to the original tension.  It takes more effort.  As these types of cookware get knocked around and chipped, etc. etc. they weaken.  That's when they "explode." 2000 reports of Visions cookware causing injury since 1983 alone (http://www.cbc.ca/ne...1-15m-1.1358284).  I can't find the original story about exploding ceramic flameware, but it's definitely been an issue there too.

 

Not an issue for the studio potter, who'd be working with the other type of body, the low-expansion type.  



#10 Benzine

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Posted 12 May 2014 - 10:21 PM

I think John posted an article a while back, about the changed Pyrex formula, and the problems people have been having because of it.

There is quite a list of how to handle and use Pyrex, that most people don't follow.
"Anything worth believing, is worth questioning"

#11 JBaymore

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Posted 13 May 2014 - 09:52 AM

I've personally seen the low expsnsion body "crack with some force" on a flame.  Not like the pre-stressed stuff though.

 

Mythbusters did a segment on the pre-stressed glass and plastic laminate side window panels on an automobile.  Interesting stuff.  They too literllay explode into tiny rounded-edge granules when hit just right.  Designed to do that to prevent sharp flying glass in an accident.

 

The real issue with flameware from the lability point that I personally see is not that it is going to suddenly "explode" with severe violence like a fragmentation grenade (the Pyrex can).  It is that it is going to be filled with very hot foodstuff in a working kitchen environment, and that it is prone to unexpected cracking due to the uneven thermal stresses. 

 

When that piece fails as it is being moved / carried, all of that hot, scalding, burning, foodstuff is potentially going to land on the cook's arms, legs, or body, on the 2 year old child under their feet, or on the much-loved family dog or cat.

 

Aside from the moral concerns involved.......... can you say "lawsuit"?

 

We certainly have the same potential risks with any food service item that we make.  A handle can come off of the cup of hot coffee at just the wrong time.  (Remember the McDonalds lawsuit... something like $4 Mil because people -of course- would not expect that hot coffee is............ hot.)

 

But the quality control over the production for flameware adds in a whole extra level of serious technical complexities.  Technically correct body formulation, accurate mixing operations of that body, precise forming operations as to thickness and stresses set up in that part of the process, accurate glaze thickness application, and precise firing. 

 

While all of the SAME things above apply to other types of food service wares for consistency of product....... we don't then try to stress the living crap out of them over a direct application of flame to part of the piece.  Typical food sercvice clay wares are not as "touchy" as flameware, and do not have to tolerate the same extremes of environment.

 

Just seems to push the risks too high for my taste (and liability tolerance).

 

best,

 

..........................john

 

PS: Benzine..... yeah.. I think I did.


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Professor of Ceramics; New Hampshire Insitute of Art

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#12 Tyler Miller

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Posted 13 May 2014 - 10:13 AM

John, wise words.  I like to think that people are reasonable and responsible when using products with assumed risk, but you're right.  Coffee's hot and people have sued over it.

 

-Tyler



#13 Rebekah Krieger

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Posted 13 May 2014 - 10:18 AM

I am getting nervous because I started creating some roasting pots (stoneware).  Is it safe to say "do not put in preheated oven, allow to cool naturally" in a product description? One other thing, I was debating over glazing the inside of the pot or allowing it to be unglazed and build up a "season" in the pot.  Do any of you have opinions on that considering this is a cookware thread? Thanks! 

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#14 JBaymore

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Posted 13 May 2014 - 12:01 PM

It seems to me that the issue here is answering the question, "How much risk are you willing to accept?"  For me, flameware is on the pernament "no-no" list.  Oil lamps are also on the "no-no" list and always have been. (Could have made a FORTUNE back in the day!)

 

For me personally there are two categories of "risks" involved: 1.) Ethical standards risks.  2.)  Legal liability risks.  Unfortunately, niether has easy answers. 

 

I'll deal only with #2 here.

 

The problem with the "do not put in preheated oven, allow to cool naturally" approach is that the description needs to stay with the piece for the useful life of the piece to help protect both you and the user.  Paper additions get lost.  Legally... I'm guessing that a sharp lawyer would contend that you should have expected that would happen to the paperwork and if the admonition was truly necessary, made provisions to warn all the users of your product not just the original sale owner.  Hang tags and product inserts DO get lost.

 

My own personal attempt at a type of solution to this liability issue a while back was to have a stamp made that said "Do not burn unattended." for some incence burners I was making.  Unfortunately that stamp on the bottom looked like crap, and tended to move the feel of the work from that of "fine craft" toward that of "commodity".  Not the idea I want with my work.  Difficult.  Fix one issue... create another.

 

Another factor in the "legal liability" side of things is how much you actually have to lose.  If you are literally a "dirt poor" (pun intended) potter......... even if someone is harmed by your product..... the liklihood of getting sued for damages is kinda' small.  To quote Janis, "Nothin' from nothin' leaves nothin'."  Such liability suits are usually "contingency fee" based, and a lawyer will usually only take one on if they see a reasonable paycheck possibility.

 

But if you are a bit more affluent, maybe because pottery is a second job to the 'big money' job, you are retired from a previous well paying career and are now doing pottery, your spouse has a high paying job, and so on... that is potentially a very different story.  Unless you are a corporation, (like a LLC) then the assets that you (and your spouse) have (homes, stocks, all studio equipment, etc.) are at risk in any potential liability situation.  Even if you "have a business" and file a Schedule C.  A sole propietorship does not protect personal assets.

 

Some would argue that having liability insurance will attract the contingency lawsuit.  A valid thought.  Again.... no easy answers.

 

If you are concerned, at the minimum get yourself product liability insurance.  The Potters Council has it for members (plug, plug, plug ;) ).  ACC has it for members.  CERF has it for members.  Any insurance agent can get it for your business.  If you are typical, it'll cost you less that $1000 a year.  Cheap really for the protection and peace of mind.  And maybe look into setting up a LLC for your pottery business; it is not hard and not expensive.

 

As to the technical side of the bakers......... you have to test them .......a lot.  Don't assume.  Do the "stupid stuff" that a consumer likely will do with it and see what happens.  They will.    Take it out of the dfreezer and put it in a pre heated oven.  Someone will.  It is for THOSE people that you have the liability insurance B)

 

best,

 

........................john


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Professor of Ceramics; New Hampshire Insitute of Art

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#15 TJR

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Posted 13 May 2014 - 02:17 PM

I make pie dishes and casseroles that go in the oven. I do not make anything for the top of the stove. All my pieces are glazed on the inside. If you were to make a chicken baker, you could leave it unglazed, soak it in water and then you get a moist bird. I have not had any explosions. I always explain about heating up slowly, and not taking pieces from freezer to oven. I do still worry about breakage though.

I am not interested in making flameware. That is what metal is for.

TJR.



#16 Min

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Posted 14 May 2014 - 02:54 PM

I am getting nervous because I started creating some roasting pots (stoneware).  Is it safe to say "do not put in preheated oven, allow to cool naturally" in a product description? One other thing, I was debating over glazing the inside of the pot or allowing it to be unglazed and build up a "season" in the pot.  Do any of you have opinions on that considering this is a cookware thread? Thanks! 

 

Nice pot! Just going to add a little of what I have found about the design of ovenware.

 

A round shape is good, pots with large flat bottoms are more prone to cracking, no sharp angles between base and walls. A couple other things that I have found help to avoid cracking are to use a low expansion clay and well fitting glaze, plus using a clay that doesn't totally vitrify. Also, having an even clay thickness throughout the pot, and not having too thick a glaze layer on the inside. You don't want any thick pooled glaze where the base meets wall. I would glaze the inside though, makes a more sanitary pot plus it evens the stress out with the glaze on the outside. Might think about the overall height of the pot, if it's too tall then the user can only use 1 rack in the oven.

 

Like John B said test the heck out of it. Put just a little bit of food in it and then stick it in a preheated oven then when hot take it out of the oven and put it on a tile trivet. Put a hot pot in a sink of water. Put frozen food in the pot then put it in a preheated oven. 

 

I still make ovenware but only for family now, they know how to use it safely. I gave up making ovenware for sale because even when I had "Care" cards with the pots I still had the odd customer let me know their pot had cracked and were disappointed. You have no control over what a customer does with the pot once it leaves your hands.







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