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toxic ?

updated tue 30 apr 96


katie rose on thu 11 apr 96

hi clayart folks,

a question has come up in the class i am taking. some of us are wondering
whether materials (such as chrome oxide, barium etc.) which are toxic in the
raw state (as when mixing glazes) are also toxic after having been fired.
in other words, could glazes which contain these "toxic" materials be safe
to use for vessels that would be intended for holding food?



katie rose

katie rose

"Love is the reflection of God's unity in the world of duality. It
constitutes the entire significance of creation." (Meher Baba)

Ron Roy on thu 11 apr 96

Hi Katie,

Depends on how durable the glaze is. Some glazes are easily attacted by
acids and sometime alkalies. Chrome has the other disadvantage of
volitizing when being fired and those fumes are the most dangerous of all.

I wrote an article once titled "All Glazes Leach" - question is how much.

I do the MSDS sheets for a local clay company and most of my information
comes from Government rules (what has to be considered dangerous) and from
the Rossol and McCann books. My brother is a biologist who is aware of the
hazards as well so I usuall check with him.

Ron Roy, Toronto, Canada

Peter and Samantha Tomich on fri 12 apr 96

Hi Ron & all clayarters this may concern,

You said you wrote an article once titled "All Glazes Leach". How can I
get a copy of this article?

What are MSDS sheets and where can I find out these Government rules
(what has to be considered dangerous).

I have your previous reference to the the Rossol and McCann books.

Does anybody else know anywhere else I can get information on toxicity
of glazes, especially barium, manganese, & lithium, as these are the in
many of the glazes we use at the community college here.

I am going to propose an independant studies topic along these lines to
one of my profs, but I'll need more resources.

I plan to try and involve the Biology and Chemistry departments here,
but I am not sure how sucessful that will be. Do any of the chemists out
there know if it would be simple to test for these substances in foods
that were cooked in ceramic vessels glazed with barium, manganese, &
lithium. If it is too complicated a process I would hesitate to ask
someone to help me in this.

Ron Roy on tue 16 apr 96

Hi Peter and/or Sam,

I have copies of the article but it is less than a page long and not much
detail. If you want a copy send me your mail address.

MSDS - Material Safety Data Sheet. Up here all suppliers must provide a
MSDS if a customer asks for one - on any product sold, clays, glazes,
stains, materials, wet clays, etc.
I beleive there is an eqivalent in the US (OSHA?)

Each product is rated according to risk (perceived, imagined, real - I'm
not in a position to know which most of the time). Clays without materials
on the "poison" list will simply have a "toxic" lable because of the
silica. Clays which have a a substance with more serious problems (Barium,
lead, manganese for instance) must have "poison" lable - skull and cross
bones. When you buy an original container of say Barium the is the poison
lable - when the supplier rebags that material they are obligated to carry
that label forward to any new container.

There were quite a few references on this list to testing facilities re
glazes. If someone has them handy would they re post them? Tends to be
pricey so get a budget.


Ron Roy, Toronto, Canada