This topic rang a bell with me as far as medicine is  concerned. 
A few interesting facts: 

Food grade cobalt is needed in the human body in small amounts. It comes from B12. 
Metal implants are made with cobalt in it - I do not know the reason, but I do know there are people whose bodies reject it. 
Cobalt poisoning comes through inhalation, the skin and when swallowed. 

In the end traces of all minerals I believe can be toxic, especially since we seldom know exactly how much we take in. The key for us potters is safe handling of all materials and to make sure our food containers and also PRESUMED FOOD CONTAINERS  are leach free.  I  added "presumed containers", because people's creativity knows no end.....when an object is hollow, it is an invitation to put food in it. 

On Thu, Aug 26, 2021 at 2:14 PM <> wrote:
People do store food in the ware we make and we have no control over that.

I do remember a barium blue mug in which the glaze on the inside was 
white about halfway up. Someone had left some "neocitron" (a vitamin C 
drink) in it on a counter over night. The drink had leached out all 
the blue and who knows what else out of the glaze.

Cobalt does not seem to be a big danger from ingestion based on what 
we know so far. Still - you don't want your ware changing colour. That 
scares people!

I wrote Eric privately - I suggested a small revision to make the 
glaze even better than it is. I wish there were more potters would 
take the time to make sure their liner glazes were stable.

I am happy to give an opinion about glaze stability. All I need is a 
recipe which I will not save or share.


Quoting Michael Wendt <>:

> I looked at the EPA web page for drinking water standards.
> Copper and Barium are both listed so I bet you can review the 
> standards for cobalt there too.
> I figured if the release level in a test is lower than the drinking 
> water standards, the release is most likely very safe since we drink 
> far more water in a lifetime than you could ever possibly release 
> into food coming into momentary contact with dishes or serving pieces.
> Worth a look if you can slog through the pages,
> Regards,
> Michael Wendt
> ----- Original Message ----- From: "Cynosure -Arts" 
> <>
> To: <>
> Sent: Tuesday, August 24, 2021 12:18 AM
> Subject: [Clayart] cobalt toxicity
> Hello - I have sent a glaze sample to the lab to test for cobalt 
> leaching and awaiting results, but I am having difficulty finding 
> online a simple number to compare the results to re: acceptable 
> leaching.  I did find one source that quoted 1.5 ppm.  Can anyone 
> point me in the right direction? I'd love to be able to confidently 
> use this glaze for food surfaces.  It passed the at-home acid and 
> alkali baths with no apparent surface change.
> thank you,
> Eric Newman
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Ron Roy
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