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oxides for safe glazes...

updated wed 10 jun 98


John Post on sun 7 jun 98

Ron Roy wrote:
>I once started a list of materials that I considered safe and other members
>of the list added to it. Anyone still have that?

This isn't the list Ron started. It's from "Keeping Clay Work Safe and
Legal" by Monona Rossol...

"WHY NOT MAKE SAFE GLAZES? The leaching problem can be avoided by
formulating stable glazes that employ only fluxes containing sodium,
potassium, calcium, and/or magnesium combined with sources of alumina and
silica. Other substances that could be used in small amounts include
sources of zinc, iron, titanium, and tin. This may not produce very
exciting or colorful glazes, but they certainly can be made stable and safe
for foodware."

So if you're trying to determine if your glazes are food safe this may be a
place to start before sending them out to a lab for testing. If you want
to have your glazes tested at a lab, here are two labs that can do the
testing. These are also from Monona's book...

Professional Service Industries
850 Poplar Street
Pittsburgh, PA 15220
412/922-4000 ask for the chemistry department

Environmental Research Inc.
309-267 W. Esplande
N. Vancouver B.C. Canada V7M 1A5
604/986-0445 ask for Bob Brown

(I have not sent anything to these two labs. I don't know how much they
charge for testing your glazes. I'm just passing this bit of info on to
the group, so those who need it can make use of it.)

John Post
Sterling Heights, MI USA

Ron Roy on tue 9 jun 98

Gavin posted me and pointed out that the list I suggested is a part of his
article on toxicty - you can all get to it at the IMC site - point you
brouser at -

It does contain more than Monona's list and there are some questionable
oxides (marked ?) - which means you should employ some science to make sure
the liner glazes made with them are stable and balanced.- a good policy for
all glazes that might come in contact with food - it makes sense from a
sales point of view to be able to tell your customers that your glazes are
designed to do the job.

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

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