Clay toxicity test for using in cookware

[Babs]

Schlemmertopf ware was all the rage in late 70s.

Roughly shaped like a dressed fowl . Inglazed "red" clay

Oil and put in oven

[Mark C.]

Research flameproof clay bodes. 

heres a thread on it as well

Robbie Lobell is very well known for this as well-If I reacll she got the formula from  Karen Karnes the potter 

and turned a business into that info.

https://www.cookonclay.com/pages/about-us

I do not think a commercial terracotta body will work for you in the long run-you will need to have additives to it.

 

One last note -a friend brought me a mug back from Mexico-He said a resturant was using them from a local potter. The mug was raku fired. Well it held water and after just a few minutes the clay abosrbed the water and was damp looking on the outside surface meaning it would absorb whatever fiuld it contained-lets say it was filled with milk. That milk would absorb into the raku body and be funky smelling in no time.You need a clay that will not do this.

[Callie Beller Diesel]

It sounds like you have some ideas about the kind of business you'd like to run, which I fully applaud. It's a much easier route to have something specific in mind and aim for it, than to make some things and see if you can figure out who to sell them to.

In terms of lab testing, the MSDS from your clay manufacturer should indicate if there are any controlled substances present, such as cadmium, lead or other metals, as they'd lead to health issues when you handle the raw material. If those metals are absent from the original clay, they won't be in the fired product to leach out. Brandywine is indeed the lab to go to if you wish to hedge your bets, as they do work specifically for potters and understand the needs. 

This next bit I want to say with the utmost respect, and again to set you up for optimal success: If you wish to make unglazed pots that are able to handle the thermal shock of being  put on a conventional stovetop, Terracotta is not a good choice. It will likely spall and not be durable under those conditions, which in itself might lead to liability issues around reasonable expectations of use. If it's unglazed, teracotta is porous, so it holds on to oils and juices that will smell and go rancid. It's a breeding ground for bacteria. If you find used unglazed chicken bricks in the thrift store, usually they smell funny. Folks have already mentioned looking into flameware, and the types of clay it uses.  @Bill Kielb or @glazenerd Are you able to suggest some good reading material regarding flameware clays vs terracotta? I think some deeper reading is a good idea for someone who needs to understand a type of clay that not everyone works with. Preeti, this is throwing you into the deep end in terms of technical information, but I believe knowledge is power. If cooking on the stovetop is your goal, you need more technical information than the average to pull it off. The good news is, it can be figured out successfully. These folks do it, and in a technically sound and and beautifully made way. (All Ginger Rogers-like). https://www.cookonclay.com/pages/green-and-healthy

Babs posted her response while writing this, and I did a quick search for Shlemmertopf, and came up with this: https://toquetips.fantes.com/schlemmertopf/. These guys have obviously been around awhile, and know what they're on about. It's interesting to note that they have liner glazes for easier sanitation and so things aren't retaining food particles or bacteria, and that they state specifically it shouldn't be used on the stovetop. Mark's reposting the thread about flameware is an excellent one and covers some good liability concerns over durability, and how terracotta can be used safely to bake in.

[Min]

@Preeti, if you want to get an idea of what the pots need to be able to handle an excerpt below by Robbie Lobbel from the April 2018 issue of Ceramics Monthly on how she tested her claybody. Try it with a lot of the pots you've made with terracotta and I think you'll find they won't survive. (Robbie Lobbel is the potter who makes the flameware in the link Callie posted above)

Link to an article on what flameware is:

https://ceramicartsnetwork.org/wp-content/uploads/2011/12/flamewaremay2011cmtechnofile.pdf

"In order to test my pots, I put them through a series of extreme temperature changes. I poured rapidly boiling water into the pots, then put them directly into the freezer. I allowed the pots to stay in the freezer overnight, where they froze into solid blocks of ice and then put them directly into a pre-heated 450˚F (232˚C) oven. The ice slowly melted and began to boil again. In his book, Clay and Glazes for the Potter, Daniel Rhodes suggests the following: “To test a body for resistance to flame, a small flat dish is made about seven inches in diameter, with a rim one inch high. Water is placed in this and it is put on an electric hot plate and heated until the water has boiled off. After five minutes of further heating, the dish is plunged into cold water. If a body survives this heating and cooling for several cycles, it may be considered flameproof” (1973 edition, page 57). I did this test too, though with one of my forms, and on a gas flame, which is a bit harder on the pot because of inconsistent heat between the flames and the burner grate." 

 

[Bill Kielb]

2 hours ago, Callie Beller Diesel said:

. Folks have already mentioned looking into flameware, and the types of clay it uses.  @Bill Kielb or @glazenerd Are you able to suggest some good reading material regarding flameware clays vs terracotta?

I do not have any special reading to suggest. In  all honesty I experimented with Robbie’s recipes and read everything associated with her story (I mean everything I could find) to see if I could become comfortable that what I made would be lasting., Most  of the wares I made were fairly bulky and depended upon the clay and a fairly heavy structure to ensure survival.  To me it was a risk I felt I could not predict and abandoned any research. I finally settled upon some personal use pizza stones and probably have 20# of low expansion clay somewhere waiting to be used. ................ Right next to the 50# of mica clay might I add.

It was something I never felt confident enough in, which is a personal choice. There are folks that seem to do it well and enjoy producing, researching and testing though.

 Reading Robbies story and trying her recipes maybe a good start, although  lithium is sort of necessary.

[Mark C.]

While on this subjct- there seems to be two kinds of stovetop wares

I have a friend with ones that are large bowl forms from Mexico -very thin and course grain clay that are fragile as they are thin. He serves warm punch in this while on a very low flame.This clay is natural occurring fron areas in Mexico and abroad. Then the more modern clay body ones formulated for the stove top like many of the above links are to.

You can web this more modern formula as I found it quickly on the web and then take it from there as Bill did above.

Lots of potential issues for sure.

Hard to improve on cast iron and other materials really.

[glazenerd]

Interesting discussion- enjoyed following it.

[Preeti]

I am overjoyed by the collective wealth of information I have received ! Thank you all ! @Mark C.  the clay you mentioned from Mexico sounds like may be perfect for my application I as a first step to proceed I would like to get hold of it and experiment like Bill suggested. I will try to search the web for sources of the clay. Please do let me know if you are aware of any.

@Min   @Callie Beller Diesel  sounds like I may have to do a lot more testing than I envisioned. Once I have things just the way I want , I will need to think about replicating it exactly each time to get things just right. Hmmm

 

[Mark C.]

I have never seen the clay from Mexico for sale .Not sure what part of Mexico but my friend usually travels to southern Mexico each year for his business.

[Preeti]

I am looking for more of a low flame crock pot like use (only for vegetarian food :-) ) So huge temperature changes or even high flames are not an immediate concern.  The liability of the pot blowing up in a customer's face is not my concern. w.r.t liability my only concern is toxicity of the food and I am thinking I could just cook in the pot and test the food for toxicity instead of being worried about the toxicity of the clay itself ?

[Babs]

6 hours ago, Preeti said:

  The liability of the pot blowing up in a customer's face is not my concern. w.r.t liability 

Just for yourself do what you like.

Selling to folk....another story.

Blowing up in faces, scalding folk I think should be in foreground of your thinking...

After leaves your hands if folk CAN put it on fast heat etc they will, no guarantee they won't and your business will be toasted.

Just saying.

 

[Preeti]

@Babs when I say is not my concern it is because I am not selling the pots as cookware :- )

[liambesaw]

7 minutes ago, Preeti said:

@Babs when I say is not my concern it is because I am not selling the pots as cookware :- )

This thread states otherwise, which would come to light during any litigation.  If you make something that looks and functions as cookware, it carries the same liability no matter your disclaimer.  

That's like making candles and saying they're for decorative use only, and not for lighting.  It doesn't hold up.  Once you sell something, you have no control over how it is used.  Our jobs as makers are to make something to the best of our ability that will not harm the user, within reason, regardless of our intended use. 

 

[Preeti]

3 hours ago, liambesaw said:

Our jobs as makers are to make something to the best of our ability that will not harm the user, within reason, regardless of our intended use. 

 

Agreed !!! most certainly.

[Rae Reich]

I may be wrong, but I believe that if  @Preeti does not intend to sell or distribute the cooking vessels, but only prepare food in them for personal use, liability would not be a problem. However, if she intends to sell that food, Health Dept rules would not permit reuse of any vessel.

[liambesaw]

8 minutes ago, Rae Reich said:

I may be wrong, but I believe that if  @Preeti does not intend to sell or distribute the cooking vessels, but only prepare food in them for personal use, liability would not be a problem. However, if she intends to sell that food, Health Dept rules would not permit reuse of any vessel.

Yeah, but their initial post says they intend on making and selling cookware.

[Preeti]

@Rae Reich yes you got it right , I intend to cook in it but also to possibly sell the food (with the cookware) .  Hence I am not worried about things blowing up in people's faces only about selling possibly toxic food.

Which is why I mentioned could i possibly just test the food for toxicity instead of the clay ?

 

 

 

[Babs]

Porous pots will heat up if microwaved...reheat food once home type of thing.

For self alone..do what you like.

[neilestrick]

18 minutes ago, Preeti said:

@Rae Reich yes you got it right , I intend to cook in it but also to possibly sell the food (with the cookware) .  Hence I am not worried about things blowing up in people's faces only about selling possibly toxic food.

Which is why I mentioned could i possibly just test the food for toxicity instead of the clay ?

 

 

 

Different foods would react differently to the toxic materials. More acidic foods will cause more leaching, less acidic would cause less leaching. Start with a safe clay and you'll be fine with any food.

[liambesaw]

Ok so from what I can deduce, you want to make cookware that serves as a plate, that will be used once and then thrown away, so you don't care about the safety of using the dish, you just need it to not poison the user...  

In that case, use a commercial clay, it's already certified nontoxic. But the good news being that in that situation, there's almost nothing that will pull any significant amount of toxins out of it from a single use anyway, assuming it's properly washed ahead of time.

[Min]

 

21 hours ago, Preeti said:

  23 hours ago, liambesaw said:

Our jobs as makers are to make something to the best of our ability that will not harm the user, within reason, regardless of our intended use. 

 

21 hours ago, Preeti said:

Agreed !!! most certainly.

 

50 minutes ago, Preeti said:

I intend to cook in it but also to possibly sell the food (with the cookware) .  Hence I am not worried about things blowing up in people's faces only about selling possibly toxic food.

Comes back to what Liam said in the quote above. You cannot control what people do with the "cookware"  once it is out of your hands. How do you stop people from using it as a single use item?

May I ask why you seem to have such an aversion to using a glaze?

[neilestrick]

Also consider what it's like to eat from unglazed dishes. When your fork hits it it's a terrible scratchy fingernails-on-the-chalkboard kind of feeling, and if you need to use a knife there's a chance you could actually end up with little bits of clay in your food, since porous clay is really easy to scratch.

[Preeti]

I think the first thing for me to do is try a few sources of clay , the one the one @Mark C. mentioned from southern Mexico sounds promising since someone is already using it for food so its likely good, maybe I will try a few terracotta sources.  I think my big challenge is going to be finding a good clay source

@neilestrick hmm the scratching :-) I suppose I am tempted to try one myself first . I see the point though.

 

[neilestrick]

31 minutes ago, Preeti said:

I think the first thing for me to do is try a few sources of clay , the one the one @Mark C. mentioned from southern Mexico sounds promising since someone is already using it for food so its likely good, maybe I will try a few terracotta sources.  I think my big challenge is going to be finding a good clay source

@neilestrick hmm the scratching :-) I suppose I am tempted to try one myself first . I see the point though.

 

The southern Mexico clay or flameware or something special like that is only going to be necessary if you're going to be cooking on a stovetop with it.  Any terra cotta will hold up fine in the oven, though, and most pre-mixed clay bodies are certified non-toxic.

[Chilly]

On 2/4/2020 at 2:34 AM, Min said:

Comes back to what Liam said in the quote above. You cannot control what people do with the "cookware"  once it is out of your hands. How do you stop people from using it as a single use item?

 

People are being encouraged to "re-use, reduce, recycle".  If something arrived containing food, it will get used for food again.  No matter that you thought it was a single-use item.  The recyclers of the world will re-use it.  For millennia.