[Clayart] cobalt toxicity

ronroy at ca.inter.net ronroy at ca.inter.net
Thu Aug 26 18:29:41 UTC 2021

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 <mwendt at wendtpottery.com>:

> 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"  
> <cynosure_arts at hotmail.com>
> To: <clayart at lists.clayartworld.com>
> 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
ronroy at ca.inter.net
Web page ronroy.net

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