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
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 <firstname.lastname@example.org>:
> 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,
> Michael Wendt
> ----- Original Message ----- From: "Cynosure -Arts"
> To: <email@example.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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