[Clayart] Cobalt toxicity

Cynosure -Arts cynosure_arts at hotmail.com
Wed Sep 1 16:29:21 UTC 2021

Thank you to all who weighed in on my earlier post (especially Ron Roy).

After much additional googling, this is the best I could find for recommended maximum exposure to cobalt taken orally:

Although the US Food and Drug Administration (FDA) has not developed an acceptable daily intake for cobalt, the United Kingdom Expert Group on Vitamins and Minerals concluded that supplementation with 1400 μg Co/d was unlikely to cause adverse health effects in adults (8). The European Food Safety Authority has suggested a safe intake of 600 μg Co/d for noncarcinogenic effects.
(American Journal of Clinical Nutrition)

Further, the EPA has NO guidelines for cobalt concentration in drinking water. for comparison.

The test I had run on the Rhodes Black glaze fired to Cone 10Redux (see glazy.com) at BSC Labs showed a result of .278 mg/L (or 278 ug).

This seems to fall well within 'safe' guidelines.....am I reading that right?

Of course, all the other variables of application and firing may make these results inapplicable for other users, but it does imply the glaze is generally acceptable as a food surface.  And I'll also add that the home alkali test (simmered in a soda ash solution) produced no surface change, so okay for the dishwasher.

Eric Newman

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