Lili Krakowski on thu 11 aug 05
Thank you all for your replies, which, in essence, confirm my intuition--or
do I mean experience? I " grew up" on the teaching that you pack a glaze
with silica to curtail crazing. At the time (Mel, glaze
calculation --pencil & paper style--was around before 1972!) coe was not
figured in/out.
I never put a glaze or clay body "on the market" at all unless it has
survived in my kitchen for quite a time, delayed crazing being such a beast.
Make sure my glazes and bodies are happy together. In fact I think too
many pots are launched without this type of testing, or why do I see so many
crazed pots in the stores?
I also am amazed how many "given" glazes in my notebooks have such LOW
silica. Weird indeed.
Anyway. Thank you all. David: will check sites. Thanks.
Lili Krakowski
Be of good courage
John Hesselberth on thu 11 aug 05
On Aug 11, 2005, at 8:57 AM, Lili Krakowski wrote:
> I also am amazed how many "given" glazes in my notebooks have such LOW
> silica. Weird indeed.
Hi Lili,
I am disappointed in this too. I have formed a theory about why it has
happened at cone 6. May or may not be right, but it fits with my
understanding of the world.
A lot of these glazes were developed in poorly insulated electric kilns
by potters who did not have a good understanding of the chemistry AND
physics of glazes. When a poorly insulated kiln is just turned off and
allowed to cool it cools too fast for crystals to form in glazes like
high calcium or magnesium mattes. But you can always get a matte by
forcing the silica low enough because you never form a good melt in the
first place. Some of the clay (or alumina) never gets into solution. So
mattes and semimattes, in particular, were developed with low silica.
There are some truly awful glazes floating around potterland. I have
several that I use as demos in workshops to show people you can pull
the color right out of them in an hour with a little lemon juice or
vinegar.
Of course there are also a lot of low silica cone 10 glazes. I'll leave
it to someone else to postulate why that happened. I would guess that
most cone 10 glazes were developed in kilns that cooled slowly enough
to allow crystals to form. Maybe it was just the easiest/quickest way
to make a matte or semimatte.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ron Roy on sat 13 aug 05
Hello again Lili,
I'm tempted to start with Once upon a time - before we understood more
about expansion - as a group - glazes were made in the empirical way - mix
up a bunch and pick the ones that looked interesting - no though to fit or
stability.
There were even those who maintained that unbalanced glazes were the only
really interesting glazes - and there still are I suppose.
A perfectly logical result if you think that understanding the technical
side of your craft is either uninteresting or/or unnecessary.
It's almost as if we are emerging from the dark ages of clay and glaze
ignorance - the wonder is - how did so many potters and pots survive in the
absence of such obvious ignorance.
RR
>I also am amazed how many "given" glazes in my notebooks have such LOW
>silica. Weird indeed.
>
>Anyway. Thank you all. David: will check sites. Thanks.
>
>
>Lili Krakowski
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
