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kmarti

Copper Carbonate And Food Safety

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I am new to the discussion, so forgive me if this topic has been debated in the past, and I overlooked it in the archive.

 

Is copper carbonate suitable for use on functional wares? I use a Turner's White base, fired to cone 8, usually in electric. I have a beautiful light green I achieve, using 1% copper carbonate in my recipe. I have researched far and wide, with many responses about the use of copper carb on food surfaces.

 

Does the copper pose a problem only when used in conjunction with certain materials or is it toxic no matter the circumstance? Also, does reduction influence the toxicity of copper carbonate?

 

All thoughts are appreciated.

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Guest JBaymore

I am new to the discussion, so forgive me if this topic has been debated in the past, and I overlooked it in the archive.

 

Is copper carbonate suitable for use on functional wares? I use a Turner's White base, fired to cone 8, usually in electric. I have a beautiful light green I achieve, using 1% copper carbonate in my recipe. I have researched far and wide, with many responses about the use of copper carb on food surfaces.

 

Does the copper pose a problem only when used in conjunction with certain materials or is it toxic no matter the circumstance? Also, does reduction influence the toxicity of copper carbonate?

 

All thoughts are appreciated.

 

 

 

kmarti,

 

Unfortunately there is no simple answer to this question that "covers all the bases". Like everything in the technical side of ceramics, the answer is always "It depends". It depends on countless sets of inter-related variables. As ceramic artists, not ceramic engineers, we are often aware of many, but not ALL of thosue variables.

 

First of all, copper carbonate will first turn into an oxide of copper when it is brought up through the heat in a kiln. That is the first part of the chemical reactions that begin to take place. Once the glaze begins melting, other chemistry takes over as to the exact nature of how the copper is disolved/bonded into the resultant fused cooled glass... and that is very specific to the precise composition of the particular glaze.

 

Extremely strong reduction could technically reduce copper oxide to the raw copper state... but that is highly unlikely in any situation except American style raku (hence the copper lusters) or the creation of true Persian style lusters.

 

Glaze chemistry software can look at a reasonable approximation of the composition of the fired glaze and make some predictions as to the nature of the potential issue with any copper present. As one of the first people to write and sell glaze calculation software for the new personal computers back in the early 80s, personally, I'd recommend Insight, by Tony Hansen if you are interested in learning about this stuff. Look up Digitalfire.com for info on that. You can download a free fully finctional demo. The Digitalfire site has a wealth of ACCURATE information....like:

 

http://digitalfire.c..._study_311.html

 

 

Next, copper is not all that toxic. That is on a relative scale, say, compared to stuff like lead and cadmium. Large doses are of real concern, but that is not the typical issue with leaching, which is more typically considered chronic and low level. Copper however does easily affect the taste of many foods..... so it can be a problem in that respect. However, if a person has Wilson's Disease (a very rare disorder) then any unplanned copper in the diet can cauce significant issue up to death. "Mainstream" medicine has one view of the effects of copper in the body, while more "alternative" medicine has another...so you have to wade through THAT issue also in making any decisions.

 

Next is the concept of how MUCH copper may actually leach out of the glaze and into any foods. At the most fundamental level, this is directly related to the precentage of the final fired glass that actually IS copper bearing. You can't leach copper out of pure melted silica wink.gif .

 

At a 1% batch inclusion of copper carbonate........ you are pretty low on the copper inclusion spectrum to start with. The place that I get kinda' concerned is with a lot of the American style Oribe green glazes with over 4% copper carbonate. I've seen them with upwards of 6% to 9% copper ..........and there is no glaze at cone 9 that is going to hold that kind of level of copper fully in solution blink.gif . The thing that makes those glazes so visually lovely... the mottling from deep green to black with a touch of irridisence, is some of the copper oxide staining some silicates percipitated out on the surfface of the glaze (copper oxide is black). On the surface and crystalline! Instant leach.

 

Another factor about leaching is the nature of the foodstuff that you are concerned with. Not much copper will leach into dry crackers on a plate wink.gif . More liquid types or "wet" foods are of the real concern. Stronger acids and bases are the bigger cuplrits than stuff with a more neutral Ph level. Orange juice in a piotcher stored in the fridge would be a good example of a problem. The longer the food is in contact with the glaze surface, the more time there is to disolve materail if it WILL disolve.

 

The definitive answer to the question is to have actual leach testing conducted. It is not that expensive. A test for only copper release will cost you about $60-70 these days.... and then you'll have a precise "scientific" answer. If you are in the US, the US government does not regulate copper release from ceramic glazes... so you don't have any legal standards to go by in that regard. The best "comparison" is to use the EPAs guide for copper in drinking water to look at the results. Then YOU will have to make a decision as to how much is too much.

 

Remember that things like glaze application thickness, the underlying clay body, and the precise firing curve can all affect the glaze melt, and therefore the potential leaching results. So the above test will only be accurate to the specific test cup, from the specific application, and the specific firing. If you can control your variables for those things tightly... than that test will be a "representative" one for your wares. If not.... leaching can (not "will") vary from the lab numbers.

 

So the good news is that a 1% and with copper.... you are not into the realy "iffy" stuff. The bad news is that to really know you'll likely have to learn a lot about ceramic chemistry and such. Which is not a bad thing if you make functional wares.

 

Also remember that the bigger hazard from ALL of the potential glaze chemistry issues is for YOU.... not the end user. Working with the raw marerials in dry powdered form in mixing glazes is more risky than eating soup out of a slightly leaching fired bowl every so often.

 

This broad subject is too complex to fully answer here.

 

 

Along with Insight, I'd recommend a few pieces of reading material for you:

 

"Keeping Claywork Safe and Legal" by Monona Rossol

 

"Artist Beware" by Dr. Michael McCann

 

"The Artists Complete Health and Safety Guide" by Monona Rossol

 

 

 

Hope this has helped instead of confused. smile.gif

 

best,

 

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

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Not intentionally trying to hijack this thread but just felt it necessary to say.....

John.... thank you for being such a vital part of this forum. Your answers seem so spot on, with the whole picture!

Not to minimize your input either, Marcia, as I have gleaned much from you as well, and many others from this forum.

I think this site has got to be one of the nicest places and most informative (media-wise) on the net. Highest of accolades

to Sherman, et al, for putting this site together, and to all that continue to make this site the gem that it is!

 

while I'm here (and hijacking...)

 

I just recently picked up my new SKUTT 1027 (here in Sweden) but have yet to wire it up and fire it. I've many test tiles drying,

in addition to the first batch of what will be hundreds of extruded border and accent tiles, all destined to finish my house

renovation. The excitement runs rampant through my body and spirit in contemplation of that first firing. Meanwhile, I feel

like a sponge, soaking up the years of experience, knowledge and wisdom from my ceramic arts gurus.... biggrin.gif

 

Interesting footnote to the SKUTT and electric kiln safety in general. Seems that nobody in this part of the world has ever heard

of a downdraft ventilation system let alone the Orton EnviroVent®, including the suppliers. So I'll be forced to build my own electric

fan downdraft system! Will probably save some serious kronor ($$$) in the process, to spend on more clay.

 

But I just want to thank you wonderful people for being so giving with your all of your accrued experiences and knowledge. It is a such

blessing for all of us (ceramic novice and otherwise) that you play an active role in this website!

 

I now return you to the previously scheduled forum topic and discussion....

 

..... Rick

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Do the slice of lemon test on any glaze you think is questionable. Put a slice of fresh lemon on the glaze and let it sit for 24 hours. If the glaze bleaches out or discolors, you have a problem.

Marcia

 

 

 

 

You can also use the vinegar test that is outlined in Mastering Cone 6 Glazes: Improving Durability, Fit and Aesthetics by John Hesselberth and Ron Roy (Paperback - Jan 2002). This will cover the acidity test for the glaze. The other end of the spectrum is the alkaline test using a concentrated dishwasher detergent. These test are not conclusive, but will give you a good understanding on the integrity of your glazes. They should not be used in replacement of a lab test, but do a good job.

 

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Mastering Cone 6 Glazes is a great handbook to understanding how glazes work. I believe John H. also mentions the lemon slice.

Digitalfire is also a tremendous help for glaze altering or tweaking glazes.. Don Hansen has done a great job there for years. I met him in Alberta in the 80s . I think Ron Roy works with him as well.

Both are good resources to use.

I also like Michael Bailey's ^6 Glazes. That is helpful in seeing what different fluxes do to colorants and surfaces.

 

Marcia

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Mastering Cone 6 Glazes is a great handbook to understanding how glazes work. I believe John H. also mentions the lemon slice.

Digitalfire is also a tremendous help for glaze altering or tweaking glazes.. Don Hansen has done a great job there for years. I met him in Alberta in the 80s . I think Ron Roy works with him as well.

Both are good resources to use.

I also like Michael Bailey's ^6 Glazes. That is helpful in seeing what different fluxes do to colorants and surfaces.

 

Marcia

 

 

I have both of them and use them often. Yes, he does mention the lemon test, but I like the vinegar test a little better. I also have been testing with the dishwasher detergent because I like my glazes to stay fresh even when put in dishwasher. Over the last 40 years I have acquired quite a library that I used in school, and when I retired-they did too, to my house! They all came out of my pocket anyway.

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Yes I have a good library in my house too. My office has a wall of shelves I built just for the clay books and magazines.

I appreciate the internet and vast access to information, but I like my books, know where to go when I need to check on something.

My Pioneer Pottery book by Cardew has been opened to the teapot spout page when leveling spouts..I am dyslexic and have to check which way to counter the torque warp.

When developing the oil burner modification, the Potters' book in a $6.98 price tag still on the shredding paper cover was full of handy information which didn't make sense until you got to the point where you ran into the problem...if you know what I mean. One of my prize books is the Three books of the Potter by Piccolpasso.

 

Marcia

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Guest JBaymore

John.... thank you for being such a vital part of this forum. Your answers seem so spot on, with the whole picture!

 

 

Rick,

 

Thanks very much for the kind words.

 

best,

 

.........john

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