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glaze leaching

updated thu 9 apr 98


Tom Buck on wed 8 apr 98

1) Iron will leach if the oxide is on the surface, which
happens with glazes overloaded with Fe2O3 (or equal). But one must ingest
quite a bit of iron for it to cause health problems (unless the person is
subject to upset by excess iron, and a small number are). What will become
clear if the user keeps putting acidic foods in the pot is the iron will
slowly disappear and expose the underlying surface, which may be good or
may be bad. Personally, I try to reserve such glazes for vases and the
like. Perhaps a plate or two.
2) Since the human body needs several (10?) milligrams of
elemental zinc (or iron) daily, zinc (or iron) crystalline glazes do not
pose a leaching/health problem if micrograms of zinc (or iron) are leached
from the pot's surface each time it is used. But again, the surface will
slowly be etched and may ruin the beauty of the crystalline glaze. Please
reserve this glaze type to non-food pots (excepting perhaps plates that
often end up as wall-hangings).

Tom Buck ) tel: 905-389-2339 & snailmail: 373 East
43rd St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of
Ontario, Canada).

On Tue, 7 Apr 1998, Laura Conley wrote:

> ----------------------------Original message----------------------------
> Two food safety glaze questions that I have not seen addressed are:
> 1) iron spots - do the iron spots that pop through some reduction fired glazes
> leach in acids?
> 2) crystalline glazes - are these food safe? I suspect they may not be soap s
> since they have so little alumina, but what about the crystals - do they leach
> acid, or once again is every glaze different?
> Laura Conley (posssibly about to put an iron spotting glaze on some plates...)
> Boulder, CO