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toxicity of glaze components

updated wed 16 jan 08


John Sankey on tue 15 jan 08

Many substances are highly toxic to some forms of life and not to
others. Two notable examples from pottery substances:

1. Copper is lethal to most invertebrates, microbes and fungi at
1 ppm single exposure, but we need half a milligram per day.
Our TOL is 20 mg/day (lifetime oral dose tolerable upper

2. Boron is lethal to chitin-shelled life - most insects -
because it makes chitin pervious to water vapour. This
mechanism doesn't affect humans. We need it only in trace
quantities; our TOL is 20 mg/day.

Lithium does not appear to be necessary for life. Oral doses of
300 mg/day are routinely used to treat human bipolar disorders
with no problems. Up to 2700 mg/day is used with intensive
medical monitoring. The toxicity mechanisms appear to be similar
to those of excess sodium and potassium i.e. cellular ionic

In short, wear a proper mask while mixing glazes and ventilate
your kiln room properly so you won't inhale them. Once they are
melted into a glaze, none of these three pose any realistic
concerns to those using our pots.

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