Philip Poburka on tue 21 nov 00
Forgive me if I am asking something that I really ought to know...I may well
have missed something...to have 'thought'... that anything fired to cone 10
was 'safe' from 'toxic' annoyances.
Is it?
Are there pesky, sub-lethal, or regretable chemical reactions/processes
going on in my Bowl of Borscht, or in me Cup of morning (afternoon, or
evening) Coffee?
I had allways supposed there were not.
At least not FROM my 'bowl', not FROM me 'cup'.
What is the fact of this matter?
Ought I to 'worry'?
(...or 'mend-my-ways'?)
Philip
in
lazzz veigh-gus
John Hesselberth on tue 21 nov 00
Philip Poburka wrote:
>Forgive me if I am asking something that I really ought to know...I may well
>have missed something...to have 'thought'... that anything fired to cone 10
>was 'safe' from 'toxic' annoyances.
>
>Is it?
>
>Are there pesky, sub-lethal, or regretable chemical reactions/processes
>going on in my Bowl of Borscht, or in me Cup of morning (afternoon, or
>evening) Coffee?
>
>I had allways supposed there were not.
>At least not FROM my 'bowl', not FROM me 'cup'.
>
>What is the fact of this matter?
>
>Ought I to 'worry'?
>(...or 'mend-my-ways'?)
Hi Phillip,
Firing to cone 10 is absolutely no assurance that your glazes won't
leach. Whether or not a badly leaching glaze will cause bodily harm is a
debated subject. There are opinions (and little or no data) on both
sides of the question. Oribe, a commonly used glaze at cone 10, is an
example of a glaze that leaches a lot of copper.
It is true that it is easier to make good stable glazes at cone 10 than
at, say 06, but it is not a given. I can make lousy (while at the same
time being attractive) glazes at any temperature. The only way to know
whether or not your glaze is stable is to test it. See the article Ron
Roy and I wrote in the September issue of Ceramics Monthly for some ideas
how to test both in your studio and in a professional laboratory.
Work is underway by me and Ron and some others to be able to better
define how to make stable glazes. If you change your mind and come to
NCECA (and bring some of your famous tools) you will be able to hear the
latest update of this.
Regards, John
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is, perhaps, still necessary to say that the very best glazes cannot
conceal badly shaped pots..." David Green, Pottery Glazes
Ron Roy on thu 23 nov 00
Hi Phil,
It is true that glazes fired higher can have more silica and alumina in
relation to flux - and therefore it should be easier to make them more acid
resistant.
Unfortunately no body has been paying any attention to what makes up a
durable glass in the last 50 years so most of the glazes we are using are
not durable. It's cause they have been chosen by how they look - and you
can't tell about durability by looking.
It looks like this is not going to change very much either - potters seem
to favour the line blending of materials to find their glazes - lots of
doing and not much thinking.
As more of us learn to use the molecular formula approach the situation
will get better. Actually it's not rocket science. I have been teaching it
for years now and it's not the only the quick and the smart who are getting
it. Much more depends on the amount of time and passion one can apply to
the task.
RR
>Forgive me if I am asking something that I really ought to know...I may well
>have missed something...to have 'thought'... that anything fired to cone 10
>was 'safe' from 'toxic' annoyances.
>
>Is it?
>
>Are there pesky, sub-lethal, or regretable chemical reactions/processes
>going on in my Bowl of Borscht, or in me Cup of morning (afternoon, or
>evening) Coffee?
>
>I had allways supposed there were not.
>At least not FROM my 'bowl', not FROM me 'cup'.
>
>What is the fact of this matter?
>
>Ought I to 'worry'?
>(...or 'mend-my-ways'?)
>
>Philip
>in
>lazzz veigh-gus
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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