[nancylee]

Hi all,
I am relatively new to the art of pottery and sometimes it is so complicated, I don't think I will ever have a handle on all of the things you can do with clay!! Slips, globes, cone 06, cone 6, sgraffitto, potash.....the list goes on and on. But one thing that I have been puzzling for a bit and cannot find a straightforward answer to, is this: can you safely eat off of low-fired goods?

The reason I ask this is because at the studio where I study, we always fire to Cone 6, and I have thought all along that it was because the things we make would be safe for food. But then I have been reading about earthenware, and that you can eat off of those goods with low fire glazes, fired to cone 05 or 06. I was just looking at some glazes that had that on them. So...am I misunderstanding something here? Can you safely eat, dishwash (which, I understand, is another question) microwave low fired goods, and if so, what is the benefit of going to Cone 6, considering how much hotter and longer that takes??

Does this make sense?? Thanks for your patience,
nancy

[bciskepottery]

Folks have been using earthenware for food storage, preparation, and eating for thousands of years. So, yes, its safe. Use durable and stable glazes -- just as you would for ^6 or ^10 wares.

Many earthenware potters advise against putting earthenware in dishwashers . . . mostly because earthenware fired at low temperatures does not vitrify and tends to be more absorbent of water. Also, dish washer detergents are far stronger than those used for hand washing and can wear down the glaze. That high absorbency can lead to explosions in the microwave (water turning to steam and steam expanding in the ware). Then, again, any clay body not fired to vitrification is susceptible to absorbing water and failing in a microwave.

If your studio is firing ^6 clay to ^6 in the kiln, it will vitrify; if they are firing ^10 clay to ^6, then the clay is going to be more absorbent and less suitable for functional ware. Some earthenware potters do fire to a higher temperature (Cone 2 or 4, for example) to more vitrify earthenware.

[Marcia Selsor]

The thing that would be "Not food safe" is a glaze that leaches. Or perhaps a surface that catches bacteria.
Temperature is not the issue.

Marcia

[nancylee]

Thank you both for that information. I really appreciate your time!
Nancy

[Chris Campbell]

Public and teaching studios tend to try to keep it simple. Bisque at 06 ... Fire at 6 or 10. This formula covers a wide range of work and keeps almost everyone productive and happy. Food safety is a benefit of a tight system like this, but not the only way to achieve it.

[neilestrick]

Low fire ware also has the possibility of harboring bacteria in the pot itself. If a glaze has crazed (crackled), liquids can seep into the porous clay, where it is difficult to clean out.

[Chris Campbell]

I really wish someone would do a proper laboratory test on this risk of bacteria growing in tiny craze lines so we could get down to the truth ... is there really enough room for the bacteria to spread in those minute cracks? ... even bacteria need room to grow. I've read articles ranging all the way from 'throw them out' to 'chill out and use them'.
If anyone has a link to a proper scientific study/paper on this, please post it! And no, please DO NOT post a flurry of opinions ... just the hard facts if you can find any.

[Marcia Selsor]

Chris Campbell, on 26 April 2012 - 10:51 AM, said:

I really wish someone would do a proper laboratory test on this risk of bacteria growing in tiny craze lines so we could get down to the truth ... is there really enough room for the bacteria to spread in those minute cracks? ... even bacteria need room to grow. I've read articles ranging all the way from 'throw them out' to 'chill out and use them'.
If anyone has a link to a proper scientific study/paper on this, please post it! And no, please DO NOT post a flurry of opinions ... just the hard facts if you can find any.

Restaurants can't use them.

Marcia

[neilestrick]

I have actually seen black stuff growing under the glaze.

[neilestrick]

I sent an email to the FDA to try and find answers to this dilemma. Hopefully they'll respond and we can get some facts. Government facts, but that's a start.

I was reading some other discussions about this topic over on the ClayArt forum, and there are a ton of opinions flying around, but no hardcore facts that I could find. Until we do get some facts, I think there's nothing wrong with opinion as long as we are clear that we are not dealing with proven facts. As with most things in ceramics, there are a million variables and experiences that guide our behaviors.

There are a lot of things I do not do in my studio because I am not willing to risk injury to a customer or lawsuit from a customer. I will not sell earthenware pottery because I am not willing to risk the dangers of bacterial growth. Those dangers include really bad things like someone getting sick, as well as annoying things like the pots turning black under the glaze from mold/bacteria/whatever which results in an unhappy customer. Until the facts are in, I will err on the side of caution.

In my opinion, the argument that "people have used earthenware dishes for years and therefore they are safe", is not convincing. There are way too many examples to refute this opinion: cigarettes, lead, asbestos, PBA plastics, bacon....

Most of the discussions I have read do not differentiate between tableware and ovenware, which seems odd to me. Ovenware may be sterilized to some degree each time it goes into the oven. Tableware does not necessarily ever get heated enough to kill bacteria unless it goes through a dishwasher. But many earthenware manufacturers recommend hand washing to prevent total saturation of the pot. So I think the earthenware bacteria discussion is really two separate discussions.

So that's where I stand. I'll let you know if I ever hear from the FDA.

[Chris Campbell]

I would be extremely interested to hear the details of where and how you saw black stuff growing under a glaze ...

[neilestrick]

It's not really that complicated. I knew someone with an earthenware pot, and there was some dark matter slowly forming under the glaze. Something had soaked in and started to get funky.

[GEP]

One of my pottery students had a cone 6 mug that oozed a black substance while it was in the microwave. The problem was that it was made with cone 10 clay, then fired to cone 6. Apparently it was growing mold inside the porous walls. So in relation to the original question of this thread, you can make unsafe pots at cone 6 too. Make sure you are using the right clays and firing properly.

So this is not an earthenware vs. stoneware issue, it's vitrification vs. undervitrification. Is there a low-fire claybody that will vitrify to food-safe levels? I bet ceramic engineers can do it if they want, whether such a clay is available to purchase I wouldn't know, but maybe somebody else does. Do I know anyone making food-safe earthenware now? No.

Mea

[Frederik-W]

I wish people would stop being overly concerned or paranoid about germs and bacteria.

It is precisely because of this middle-class fear that more and more kids develop all kinds of allergies and immune problems.
It is called the "Hygiene Hypothesis" and is now well supported by scientific studies.
We try to live in an environment that is too clean, so our immune systems do not get primed to develop properly.
Advertisements for cleaning products thrive on creating a health fear if you don't live in a 100% germ-free environment. And laywers thrive on suing everyone for anything, especially in the US.

"Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world".
etc. etc etc.
A while ago I read yet another study proving that farm kids have far less immune problems than city kids because they come into contact with germs.

There is nothing wrong with using earthenware!

[Matt Oz]

As to the original topic, I would like to take a crack at giving someone new to pottery some practical advice. I am also referring to commercial clay bodies and things common to classrooms.

yes, perfectly food safe low fire pottery in the cone 06-04 range is made every day, and lots of potters have great success with it, but in general (yes there are exceptions) low fire pottery is not considered as strong and durable as cone 6 – one reason being that it is so porous, and also not recommended for microwaves.

So for functional ware, a lot of potters choose to fire to cone 6 or higher. Properly fired, it will be denser and less porous than your typical low fire clay, along with other factors, this makes it stronger. Even the glazes are considered more durable.

To make sure your pottery is suitable for microwave or oven use, that is a whole other discussion.

OOPS, I think I mostly repeated what bciskepottery already said, oh well couldn't hurt.

[nancylee]

Matt Oz, on 27 April 2012 - 06:36 AM, said:

As to the original topic, I would like to take a crack at giving someone new to pottery some practical advice. I am also referring to commercial clay bodies and things common to classrooms.

yes, perfectly food safe low fire pottery in the cone 06-04 range is made every day, and lots of potters have great success with it, but in general (yes there are exceptions) low fire pottery is not considered as strong and durable as cone 6 – one reason being that it is so porous, and also not recommended for microwaves.

So for functional ware, a lot of potters choose to fire to cone 6 or higher. Properly fired, it will be denser and less porous than your typical low fire clay, along with other factors, this makes it stronger. Even the glazes are considered more durable.

To make sure your pottery is suitable for microwave or oven use, that is a whole other discussion.

OOPS, I think I mostly repeated what bciskepottery already said, oh well couldn't hurt.

Thank you - saying things a few times, in different ways, is always helpful. I appreciate the knowledge shared,
Nancy

[OffCenter]

Chris Campbell, on 26 April 2012 - 12:51 PM, said:

I really wish someone would do a proper laboratory test on this risk of bacteria growing in tiny craze lines so we could get down to the truth ... is there really enough room for the bacteria to spread in those minute cracks? ... even bacteria need room to grow. I've read articles ranging all the way from 'throw them out' to 'chill out and use them'.
If anyone has a link to a proper scientific study/paper on this, please post it! And no, please DO NOT post a flurry of opinions ... just the hard facts if you can find any.

If you were the size of bacteria those craze lines would look like the Grand Canyon.

Jim

[DAY]

Not all “bugs” are bad; your gut is filled with friendly little folks that digest your food. TV has lately discovered that they can sell you the same bacteria, (“ProBiotic”) in packaged form!




Milk is Pasteurized to kill microorganisms (such as Brucella, Campylobacter, E. coli, Listeria, Mycobacterium bovis, Salmonella, etc.

It can be done in 30 minutes at 145F, or “flash” pasturized at 165F for 15 seconds. Your dishwasher gets hotter than that.




Lead glazes are another whole “food safety” topic.




The biggest danger of food safety in ceramics is- in America, at least- lawsuits. That is why restaurants have different criteria for their dinnerware.




Relax- and look both ways when crossing the steet, you’ll live a long time.

[Chris Campbell]

Our customers use our wares in ways we could not imagine ... so I guess we should always default to worst case scenario.

And UGH! ... Am I ever sorry I asked a out the black gunk growing under glaze ... TMI.

[neilestrick]

I sent an email to the FDA asking about studies relating to the food safety of non-vitreous pots due to bacterial growth, etc, as well as rules regarding restaurants being able to use them. Here's the reply:

Mr. Estrick, I don't have information on what restaurants use. This would be up to the state health department. FDA does not have study data related to this issue. The dishes would have to comply with the food contact substance regulations and the manufacturer must assure that its use is safe.

In reading through the food contact substance regulations, it seems that they only apply to materials leaching out of the material, not its ability to be cleaned/sterilized. I've sent another email with further questions regarding how they classify reusable vs single use items, if at all, like ceramic dinner plates vs paper plates. Does one have to prove that a reusable item can indeed be cleaned/sterilized? Can any porous item be considered legally safe for food use? I'll let you know what they say.

I've also contacted the state of Illinois (where I live) to get their opinion on this matter. I'll post their reply as well.