Alisa Clausen on mon 22 sep 03
> You said:
> > Glazes do, in many instances, serve an important practical function
> > by making the surface impervious to liquids.
Dear Malcolm,
If I had to chose one soap box for ceramic myths, I may chose this one
subject.
Virtrieous clay makes a pot water tight, not the glaze over the clay. If a
clay body is underfired and glazed, the pot is not water tight. The water
will eventually seep out of the fired clay body and rest inbetween the pot
and glaze. Eventually (one month, ten years?) the glaze will lift off the
pot. If the glaze is crazed (many times the crazing is not visible to the
naked eye) the water will get inbetween the clay and glaze as well as seep
through the glaze layer. The glaze will lift off the pot in a relatively
short time if the water is in between the pot and the glaze is subjected to
thermo expansion, i.e. the pot is outdoors in freezing climates.
The idea that a glaze seals a non vitreous clay type is perhaps believed to
be true by many, but is not true.
I was put so much in doubt about what I had learned, I was greatful when
Tom Buck helped to set me straight again.
regards from Alisa in Denmark
Malcolm Schosha on mon 22 sep 03
Alisia,
I said that glazes make surfaces impervious to liquids. This is
correct. I did not say pots last forever. They do not. Not
earthenware, not stoneware. I have seen stoneware glazes also develop
very serious problems if they are used to hold liquids over time.
This is natural, nothing lasts for ever. I have also seen, in
museums, Rembrandt paintings that have developed terrable problems
with the paint. Does that make the painting any less an art treasure?
I have made plenty of stoneware and porcelain, but like earthenware
better. I know that porcelain is harder, but that does not (in
itself) give it artistic supriority. If there is any "ceramic myth",
it is that harder material gives a superior product artisticly. That
idea is rediculious.
Malcolm
......................................
--- In clayart@yahoogroups.com, Alisa Clausen wrote:
> > You said:
> > > Glazes do, in many instances, serve an important practical
function
> > > by making the surface impervious to liquids.
>
>
> Dear Malcolm,
> If I had to chose one soap box for ceramic myths, I may chose this
one
> subject.
>
> Virtrieous clay makes a pot water tight, not the glaze over the
clay. If a
> clay body is underfired and glazed, the pot is not water tight.
The water
> will eventually seep out of the fired clay body and rest inbetween
the pot
> and glaze. Eventually (one month, ten years?) the glaze will lift
off the
> pot. If the glaze is crazed (many times the crazing is not visible
to the
> naked eye) the water will get inbetween the clay and glaze as well
as seep
> through the glaze layer. The glaze will lift off the pot in a
relatively
> short time if the water is in between the pot and the glaze is
subjected to
> thermo expansion, i.e. the pot is outdoors in freezing climates.
>
> The idea that a glaze seals a non vitreous clay type is perhaps
believed to
> be true by many, but is not true.
> I was put so much in doubt about what I had learned, I was
greatful when
> Tom Buck helped to set me straight again.
>
> regards from Alisa in Denmark
>
>
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Alisa Clausen on tue 23 sep 03
Dear Malcolm S.
> I said that glazes make surfaces impervious to liquids. This is
> correct.
That is not correct.
Impervious means according to the English dictionary and I as understand the
word in your post;
not allowing entrance or passage (i.e. impenetrable)
not cabable of being damaged or harmed (i.e. a coat to rain, a carpet to
rough treatment)
not capable of being affected or disturbed (i.e. to criticism)
I understand in your post this word to simply mean water tight or sealed.
If we agree that these words are interchangeable in your post, then the
theory is incorrect.
I think it is a mistake to bend facts through art talk- intellectual wars or
stubborness, that are important for basics of the craft, to satisfy a
personal feeling of being right.
"I did not say pots last forever. "
This is something you did not say, nor did I reply to.
As we know, facts change also, over the years, due to new research.
However, to date, I have not heard about any new research on this subject to
alter the fact that pots are only water tight if the clay is vitrified.
It would be a hard task for me to disregard the knowledge of Tom Buck.
regards from Alisa in Denmark.
Ian Currie arrives today. We are holding the workshop this weekend. Very
exciting!
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