Michael McDowell on sun 26 apr 98
Glaze Gurus,
I was just daydreaming today about putting together a pamphlet or something
to explain some of the extra lengths I go to in pursuit of the highest
quality for my ware. Amongst those aspects of my work are the efforts I have
expended in eliminating crazing and precautions against the leaching of
harmful chemicals into food and drink. I had always conceived of these as
separate issues that both needed to be addressed in the quest to make the
"best" that I can. But in my ruminations today I thought that crazing must
substantially increase the amount of glaze surface exposed to leach from.
Wouldn't that mean that for any given glaze formula it's solubility would be
substantially less if the glaze fit the clay body used? Does anyone use that
as an argument for eliminating crazing from ware?
Michael McDowell
Whatcom County, WA USA
http://www2.memes.com/mmpots
mmpots@memes.com
Ron Roy on tue 28 apr 98
Hi Michael,
The quick answer is no.
Stand by for the long answer.
If a glaze is not durable and material is coming out then - because there
is more surface to be attacked because of the cracks in the glaze - then
crazing accelerates that process. You can say more will come out sooner.
If we are looking at a durable glaze we have a much different situation.
Even though there is more surface area to be attacked - lets say by an acid
- then - because the release is small - there is not much difference.
It is true that all glazes leach - even the most durable - the amount of
leaching is what makes the difference between what is considered a durable
and less than durable glaze.
Well maybe the slow answer is yes - the word "substantially" is the problem
here. In a soft glaze the answer is yes - more leaching. If the glaze is
durable the answer is not any significant amount more.
>I was just daydreaming today about putting together a pamphlet or something
>to explain some of the extra lengths I go to in pursuit of the highest
>quality for my ware. Amongst those aspects of my work are the efforts I have
>expended in eliminating crazing and precautions against the leaching of
>harmful chemicals into food and drink. I had always conceived of these as
>separate issues that both needed to be addressed in the quest to make the
>"best" that I can. But in my ruminations today I thought that crazing must
>substantially increase the amount of glaze surface exposed to leach from.
>Wouldn't that mean that for any given glaze formula it's solubility would be
>substantially less if the glaze fit the clay body used? Does anyone use that
>as an argument for eliminating crazing from ware?
>
>Michael McDowell
>Whatcom County, WA USA
>http://www2.memes.com/mmpots
>mmpots@memes.com
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
Michael McDowell on wed 29 apr 98
Hi Ron,
How's that mug I sent you holding up? If I follow the trail of your
reasoning in you response to my musing correctly, then you agree with me to
some extent. You're just uncomfortable with the phrase "substantially more
leaching" being applied to a durable glaze. That's understandable since the
definition of a durable glaze is one that does not leach substantially. I'm
afraid my Economics training is showing now when I suggest we focus at the
margin. If we took a glaze that just barely qualified as durable (there must
be some cutoff point) when properly fitted to a clay body. MIght that glaze
then be classified as non-durable if it was used on a clay body where it was
quite crazed?
In practice, I wonder how many of us know whether our glazes qualify as
durable. It is not so easy to determine as whether or not it fits. Of course
we can spot really obvious cases with the "vinegar test", but we'd really
need to send our work out to labs for testing to be absoloutely sure our
glazes were durable. We can follow the guidelines the limit formulas offer.
That can give us some security, perhaps even protect us from a lawsuit, but
not certainty. And don't we love to push those limits? Maybe we have three
sets of limit formulas and a glaze that falls within only one of those sets
of limits. Or maybe we excuse a slight extrapolation since the limits are
for cone 10 and we're going to 11...
I take it as a given that I will not be sending my glazes off for testing.
Budjet constraint. But I do try and stay close to the limits, hoping for a
durable glaze. But if I'm using fluxes or colorants that may be harmful if
ingested, I'll worry.
It seems a comfort to think that however durable my glazes are, they'll be
more durable thanks to the fact that I'm eliminating crazing. Do you have a
problem with that? Your post follows...
Date: Tue, 28 Apr 1998 10:04:04 EDT
From: Ron Roy
Subject: Re: Might Crazing Promote Leaching ?
----------------------------Original message----------------------------
Hi Michael,
The quick answer is no.
Stand by for the long answer.
If a glaze is not durable and material is coming out then - because there
is more surface to be attacked because of the cracks in the glaze - then
crazing accelerates that process. You can say more will come out sooner.
If we are looking at a durable glaze we have a much different situation.
Even though there is more surface area to be attacked - lets say by an acid
- then - because the release is small - there is not much difference.
It is true that all glazes leach - even the most durable - the amount of
leaching is what makes the difference between what is considered a durable
and less than durable glaze.
Well maybe the slow answer is yes - the word "substantially" is the problem
here. In a soft glaze the answer is yes - more leaching. If the glaze is
durable the answer is not any significant amount more.
Ron Roy
Michael McDowell
Whatcom County, WA USA
http://www2.memes.com/mmpots
mmpots@memes.com
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