iandol on wed 23 apr 03
Dear Friends,
I think the question of the behaviour of glazes which contain the =
Element Lithium is wide open.
I have used a glaze rich in Soda Felspar (52%). Because it has a =
tendency to craze with 65% Na-felspar it is dosed with Petalite (13%). =
It is a colourless, transparent, smooth, high gloss glaze, fired to a =
temperature and for a time which ensure consistency of those qualities. =
It mimics obsolete Lead glazes in appearance, a deep lustrous surface. =
For more than ten years we have used Coffee Mugs twice a day which are =
lined with that glaze. They go into the microwave each time they are =
used and are washed afterwards in hot water. There is no apparent =
deterioration. Our food bowls are also treated with that glaze, inside =
and out. They also retain their brilliant surface. NO signs of etching =
or abrasion.
Sodium, known to dissolve out of the minerals which contain it (We chat =
about Neph Sy!! deflocculating glaze slop), is bad for people with heart =
conditions or hypertension. Potassium ions like Sodium ions are soluble. =
An excess can upset the electrolytic balance of body fluids and lead to =
problems with the nervous system. Do we consider excluding them from our =
ingredient list? Never heard a word against either on the grounds of =
health!
Do I have reservations about using suspect elements? Yes.
I would not use a glaze which was mat or opaque to line domestic or =
table wear. Two reasons.
First: It is difficult to discriminate between opacity and/or matness =
due to recrystallisation or insolubility. Lower firing temperatures =
exaggerate this problem. Shorter firing time exaggerate this problem.
Second: There is no way, other than by a laboratory test, which can =
provide evidence of dissolution. The Organic Acid test Ron and John =
recommend is a useful indicator. But the solutions obtained from those =
investigation need to be analysed or tested to establish the nature and =
quantity of those elements which have been removed from a glaze.
Testing and education are the only ways to reach a depth of knowledge =
and wisdom which enable us to distinguish fact from folklore.
Best wishes to all,
Ivor Lewis. Redhill, South Australia.
Edouard Bastarache on thu 24 apr 03
Hello Ivor,
"Sodium, known to dissolve out of the minerals which contain it (We chat
about Neph Sy!! deflocculating glaze slop), is bad for people with heart
conditions or hypertension. Potassium ions like Sodium ions are soluble. An
excess can upset the electrolytic balance of body fluids and lead to
problems with the nervous system. Do we consider excluding them from our
ingredient list? "
Very fine observation, for those who do overkill about about the problem
of glaze leaching.
Later,
"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
Ron Roy on sat 26 apr 03
This a good argument for using stable glazes as liners of course - and a
good argument for understanding the different levels of toxicity of the
elements we use.
I am beginning to get the feeling that many potters don't want to know
because they feel their best glazes will no longer be acceptable and they
don't have the knowledge they need to fix em.
Try to understand your craft - there are infinite posibilities - we are
going through a revolution in understanding glazes. There are many potters
who are beginning to understand how to make better glazes. There are also
many who cannot or will not learn. They will kick and scream and use words
to imply there is nothing to worry about - as it is with all revolutions
and always will be.
RR
>"Sodium, known to dissolve out of the minerals which contain it (We chat
>about Neph Sy!! deflocculating glaze slop), is bad for people with heart
>conditions or hypertension. Potassium ions like Sodium ions are soluble. An
>excess can upset the electrolytic balance of body fluids and lead to
>problems with the nervous system. Do we consider excluding them from our
>ingredient list? "
>
>
>Very fine observation, for those who do overkill about about the problem
>of glaze leaching.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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