Evaluating toxicity in glaze for teaware

[thiamant]

Hi potters!

What do you think about using copper saturate glazes (say 5%) or barium in glazes that will just be used for teacups, teapots, etc? Since there are no acidic foods in contact and no dishwasher what confidence might we have that the glazes wont leach toxic substances? What about using them just on the outside?

[Mark C.]

I use a barium glaze on the outside (not the lip that you drink out of) of a few wares. I use a white liner on inside and lip in thesse situations .All cone 10 reduction fired .

[Hulk]

I went liner glaze on almost all interiors (anything that can hold liquid, food, or living things) and stable, reliable glazes everywhere else.

[Callie Beller Diesel]

Definitely stick to using a durable liner. I have a set of wine glasses that are lined with a barium matte from the 90’s from a friend. (I know, I know.) They’ve held wine twice, and are stained all to heck. They are mostly sculptural and sit on a shelf. 

[liambesaw]

I'd think tea would be acidic enough to pull copper from a glaze.  Barium is a trickier beast that requires special chemistry and firing to be durable.  I'd say no to a barium matte at cone 6 oxidation because from my research it is not possible to make this durable.

[Callie Beller Diesel]

Depending on the saturation level, yes, copper will give the tea a metallic taste. :p

 

[Bill Kielb]

I have to return all the items below! Just kidding, interesting though. Not to minimize this issue because I am a durable liner type glaze advocate and don’t use barium or vanadium but a good read might be some work presented at NCECA 2016 on copper solubility, toxicity, etc..... https://www.ceramicmaterialsworkshop.com/uploads/5/9/1/2/59124729/031218-peter_berg-final_draft.pdf

 

[liambesaw]

2 hours ago, Bill Kielb said:

I have to return all the items below! Just kidding, interesting though. Not to minimize this issue because I am a durable liner type glaze advocate and don’t use barium or vanadium but a good read might be some work presented at NCECA 2016 on copper solubility, toxicity, etc..... https://www.ceramicmaterialsworkshop.com/uploads/5/9/1/2/59124729/031218-peter_berg-final_draft.pdf

 

The issue isn't with the copper itself, it's with the copper causing a softening of the otherwise durable glaze iirc.  You could actually eat copper carbonate and live just fine  (edit: don't eat copper carbonate)

[Bill Kielb]

2 hours ago, liambesaw said:

You could actually eat copper carbonate and live just fine  (edit: don't eat copper carbonate)

You might find the study interesting, including the durability aspects as well as the ingestion part.

[liambesaw]

59 minutes ago, Bill Kielb said:

You might find the study interesting, including the durability aspects as well as the ingestion part.

Well they say their test yielded zero copper release but then post that almost 1 gram per liter leached into the acid with their matte glaze at 5% copper cone 6, and only 173 milligrams with 3% copper.  I'd say that's quite a bit of durability loss at 5%.  

But the also say that their matte glaze also was more durable than their glossy, so I am not really computing what they're trying to say, other than copper is safe in glazes because it's not really that toxic.

[Bill Kielb]

Just now, liambesaw said:

But the also say that their matte glaze also was more durable than their glossy, so I am not really computing what they're trying to say, other than copper is safe in glazes because it's not really that toxic.

Definitely anomalies in testing but even using as a worse case it’s nearly impossible to ingest enough without experiencing hyponatremia first. So some interesting data in durability, potential dissolution, maximum permissible toxicity etc.... Need more study for sure  but lots of aspects of this are a bit opposite of mainstream thinking.

I always wondered about those high end copper vessels or all that copper pipe our drinking water exists in. Just sayin, pretty interesting.

[liambesaw]

25 minutes ago, Bill Kielb said:

Definitely anomalies in testing but even using as a worse case it’s nearly impossible to ingest enough without experiencing hyponatremia first. So some interesting data in durability, potential dissolution, maximum permissible toxicity etc.... Need more study for sure  but lots of aspects of this are a bit opposite of mainstream thinking.

I always wondered about those high end copper vessels or all that copper pipe our drinking water exists in. Just sayin, pretty interesting.

Well there's also a pretty big difference between metallic copper pipe alloys carrying buffered water and copper oxides and carbonates in glaze.  And if your water isn't buffered, well, look at some of the places in the country having some awful problems with lead in the water right now.  Acidic tap water is real bad for pipes and solder.

[Bill Kielb]

8 minutes ago, liambesaw said:

Acidic tap water is real bad for pipes and solder.

Interesting as I am very familiar with lead service main replacement and some of the programs in place. We are currently actively replacing these in the city of Chicago. Soft water is the difficult one actually, most drinking water ph is pretty reasonable. Same for most piping systems, soft water, very aggressive .......... velocity erosion becomes a real thing.

[liambesaw]

Just now, Bill Kielb said:

Interesting as I am very familiar with lead service main replacement and some of the programs in place. We are currently actively replacing these in the city of Chicago. Soft water is the difficult one actually, most drinking water ph is pretty reasonable. Same for most piping systems, soft water, very aggressive .......... velocity erosion becomes a real thing.

Yep, and really bad for pvc as well.  My tap water from the city is generally extremely soft, 20ppm tds, and I've asked the city about it, but it's river water in the northwest and they are averse to adding minerals.

So far so good though, and I have no copper piping in my house, but I know the mains are all probably steel. It'll catch up with them some day.

[Bill Kielb]

25 minutes ago, liambesaw said:

So far so good though, and I have no copper piping in my house, but I know the mains are all probably steel. It'll catch up with them some day.

In the Midwest copper piping is the 100 year house piping. Pex  etc.... 80 year.  Locations treating river water, typically soft and aggressive. Water IS the universal solvent. I usually point to the Grand Canyon as an example. Interestingly we no longer solder with 50/50 (lead/tin) solder. 95/5 has become popular and pro press fittings and a hydraulic press. Not sure what sealant in the pro press fittings is made of though. Maybe they are 80 year fittings

BTW - mains generally range from wood to ductile iron for modern stuff.

[thiamant]

9 hours ago, Bill Kielb said:

I have to return all the items below! Just kidding, interesting though. Not to minimize this issue because I am a durable liner type glaze advocate and don’t use barium or vanadium but a good read might be some work presented at NCECA 2016 on copper solubility, toxicity, etc..... https://www.ceramicmaterialsworkshop.com/uploads/5/9/1/2/59124729/031218-peter_berg-final_draft.pdf

From the document:

Copper toxicity comes from chronic exposure to copper. Under normal conditions, the body and process and expel copper, but excess exposure over a period of time will result in decreased liver function and possible eventual Hepatitis. The Center for Disease Control has documented that that the limit for copper toxicity is 550mg of copper per kilogram of body weight per dayviii. This translates to a 150lb (68kg) person, being able to consume up to 35,750 mg of copper per day, without suffering chronic effects. It is important to place these values in context of pottery exposure, to establish how much liquid one would have to drink to begin to suffer from the effects of copper toxicity. The first question is how much actual copper is in, say a mug? Based on an application gram weight of 0.5 grams per square inch (industrial standard), and a surface area od 37.36 square inches for a 3’x’3.25” cylindrical mug. A 5% copper mug would be normalized to 4.76% of the composition, and that copper carbonate is only 64.4% copper (the remained is CO2) The glaze application for the mug would only have 590.4 mg of copper, total. That also assumes that the liquid from that leaching would extract 100% of the available copper, which is only realistic for the absolute poorest glazes. Even so it will still only equate to the one day expose for a one pound creature. A 150lb (68kg) person would need to drink 39.6 liters of copper contaminated water from our worst performing sample (Cone 6, Matte at 5% copper carbonate) to approach chronic toxicity exposure for a single day. For reference, the average human male drinks 3.7 liters of liquid, total in a dayix.

 

Quite revealing:

Basically you would have to drink so much water that it would be easier to simply die of water poisoning...

 

[Bill Kielb]

1 hour ago, thiamant said:

Quite revealing:

Basically you would have to drink so much water that it would be easier to simply die of water poisoning...

Definitely interesting and explains my dilemma with copper pipes etc.... but does conclude with “Context for our materials will always be the relevant factor when considering toxicity. Glazes should be designed and fired for maximum durability and quality at all times.”

[thiamant]

We could also talk about the presence of heavy metals in fish like salmon, tuna, etc ...

[Babs]

And straws that break camels backs.

Better to have a durable safe liner flaze and lip with fancy glazes on outside.

[Callie Beller Diesel]

Notice that when I posted, I wasn’t mentioning toxicity: I was mentioning durability. Potters are unlikely to poison anyone other than themselves. But that is no excuse for workmanship you know isn’t as good as it should be..

 

[Bill Kielb]

1 hour ago, Callie Beller Diesel said:

I was mentioning durability

Nice catch! I posted the study because it has some incredibly pertinent info on general durability of glazes. Not many folks tend to notice.

[Callie Beller Diesel]

That part of the study needs to be expanded. I’d be interested in the results.

[liambesaw]

8 minutes ago, Callie Beller Diesel said:

That part of the study needs to be expanded. I’d be interested in the results.

That was my issue with the paper, it contradicts itself quite a few times in the durability section.  

[Bill Kielb]

30 minutes ago, liambesaw said:

That was my issue with the paper, it contradicts itself quite a few times in the durability section.  

I found the flux ratio to be significant, the gloss / matte as si:al, the colorant as flux representation which is something the extended UMF is beginning to cover and the overall toxicity issue interesting as well as the general trends very interesting.

[liambesaw]

35 minutes ago, Bill Kielb said:

I found the flux ratio to be significant, the gloss / matte as si:al, the colorant as flux representation which is something the extended UMF is beginning to cover and the overall toxicity issue interesting as well as the general trends very interesting.

Yeah but if it says the ratio made the glazes durable with no leaching, but then a few paragraphs later talked about how they leached quite a lot.  So that throws the entire premise out the window in my book.  I do believe that the most durable glazes keep within that range, but obviously copper had a very large affect on the durability, so their premise that copper would not affect durability is false.