Clay toxicity test for using in cookware

[Callie Beller Diesel]

For those who remember another page to this thread, fear not. The conversation was getting very technical, and was going well beyond the scope of the original question. In the name of not overwhelming beginners who might be encountering this thread now or in the future, we've split some of the conversation into it's own topic.  Should any wish to go down a clay testing rabbit hole, you can follow along here.

Callie and The Moderator Team

[liambesaw]

1 hour ago, S R Sharma said:

Hi, I am a soil researcher and an MEC cook! And I am shocked to see the foul gossip being spread about an amazing company.
As a person who studies soil and as a person who is cooking food in the healthiest cookware, let me tell you somethings:
1.    Miriam's Earthen Cookware uses primary clay. Please note-- you can hardly find any clay in Boston as it is so densely built up. And primary clay cannot be obtained from topsoil, you must dig at least 15-20 feet below topsoil!
Their clay is harvested from very remote areas (far away from Boston off course!) and from under 20 -30 feet of topsoil. Also, they make sure there are no manufacturing industries or farming within a 15-mile radius 2. Primary clay is more elastic then tertiary or secondary clay and with the right techniques, can be formed into ware without additives.
2.    It is 100% pure and edible. I know people who eat bentonite clay for health reasons, this is purer than bentonite!
3.    Their clay is tested using the Morgan soil testing system. This is one of the best and reliable tests out there for testing soils.
4.    Just like stone is a natural product of earth, Miriam's Earthen Cookware clay decomposes and weathers back into the soil WITHOUT causing disruption to its bio-chemical balance. That is what they mean by saying it is 100% compostable and biodegradable. (after cooking food in it for years, bacterial decomposition is possible when discarded).
Why these lies? and why all this envy? It is not good for your health! Oops, let me not say that, I take that back, lest I stand a chance of being sued!
Have a nice day!

Primary clay is not as plastic as secondary and tertiary clays.  For instance, ball clay is secondary and bentonite is tertiary.

Fired clay is neither biodegradable nor compostable.  There is no biological process that breaks down ceramic, there is no carbon available.  The only thing that breaks down ceramic is physical force, ie. erosion, milling.

I'd think a soil researching would know these things...

 

 

[Callie Beller Diesel]

It’s not envy, believe me. And no one’s lying. 

While I can appreciate anyone being enthusiastic about a product they love, I dislike it when incomplete information leads people to inaccurate conclusions. Especially when people are being sold something. So there are a few things I’d like to supplement your understanding with here. Note that I live in a country where this cookware isn’t available, so I have no vested interest in Miriam’s business one way or another. MEC here refers to a camping supply chain. Please note that I am not suggesting that Miriam’s cookware is of poor quality, or that you shouldn’t use it. Indeed, if she’s making pots that can be used on a stovetop, they’re probably reasonably durable.  I do take issue with the way she markets it as being healthier than other products.

So. On to some expanded information that you can do with as you wish.

-Primary clay is for the most part, not more elastic than secondary clays. Geologically, clays are formed by erosion. Primary clays are defined as being found closer to the parent rock, as having a larger particle size and as being mixed with fewer minerals from other sources. They do tend to have fewer things such as iron, other metals or minerals because of that, but if any of those materials were present in the parent rock, they will also be present in the resulting clay.  Secondary clays tend to be mixed from more than one source, are further from the parent rock, and have smaller particle sizes because they’ve been eroding longer. The smaller particle size of secondary clays is what gives them greater plasticity, as well as a greater shrinkage rate. All clays in these categories vary, depending on the composition of the parent rock, if they’ve been further processed after digging, and how far from the parent rock the clay forms. It is possible to have plastic kaolins (a form of primary clay), and it is possible to have ball clays (secondary clay) with larger particle sizes. Primary, secondary and tertiary are just descriptors, not value judgements. One is not better than the other. They are often combined in pottery clays to take advantage of the desired properties of both.

-Elasticity or plasticity is also a relative and arbitrary measurement when it comes to making pottery. Elasticity alone does not make a clay suitable to make pottery with, although it’s desirable as long as it’s within a certain range. Plasticity is totally irrelevant to the end user of the pot. It’s a quality that’s only important to the potter.

-You don’t always have to dig very deep to obtain nice clays. It depends on the overburden depth, which varies with geography. Clays can come from riverbanks or the exposed sides of hills. They may only be covered with a few inches of overburden. You don’t generally obtain ANY clay, primary or otherwise from the overburden unless you’re engaging in a bit of a backyard passion project. It’s too full of organic material and humus that needs to be screened out to be practical, especially for a business.

-Clay may be edible, but it isn’t very digestible. Many mixed clays sold for pottery purposes in Canada and the US can be consumed in small quantities without experiencing anything worse than some minor constipation. But just because you can, doesn’t mean you should. Bentonite especially will absorb water and swell in the digestive tract. That’s why they tell you to drink lots of water if taking bentonite for a cleanse, or you can do yourself some real damage. There are also many grades of bentonite, as the mineral is used in a number of industries. It’s found in cosmetics, as filler in medications, and in cat litter, just to name a few products. Pure isn’t a helpful description in this instance, although it’s an evocative word.

 -The assorted Morgan testing methods are used to determine minerals available to plants in farming soil. This is highly useful information if you are growing produce or raising livestock. But tests done on the raw clay are going to have very little bearing on the finished piece. Once clay is fired it becomes ceramic, and isn’t soil by any technical or practical definition anymore. Its chemical structure has been changed, and organic materials like carbonates or sulphur have burned off. It’s a different substance with new properties at that point.

- Stone isn’t compostable or biodegradable, nor is ceramic.  The ASTM defines compostables as anything that undergoes degradation by biological processes during composting to yield CO2, water, inorganic compounds and biomass at a rate consistent with other compostable materials and leaves no visible, distinguishable or toxic residue. Biodegradables are anything that undergoes degradation resulting from the action of naturally occurring microorganisms such as bacteria, fungi, and algae.  Ceramic material isn’t broken down via microorganisms, especially if they’re durable enough for stovetop use. There are potshards that have been found in prehistoric archeological digs that have been reassembled into vessels. There is no biomass intrinsic in ceramic material. There is also no carbon or water present in its structure. Ceramic material can erode, but that will take an amount time measured in geologic units. I will agree though, that potshards are unlikely to be harmful to the environment.