kat on sun 17 apr 05
Des said:
"...That said a non porous, non absorptive cone 11-12 body with a crazing
glaze has to be much stronger than for example
a non crazed one at cone 6 ;-) ..."
Des
That is a very interesting comment. Some time back I was involved in doing
some MOR
tests. (jeeps - that technician side of me is resurfacing.) The results
were quite simple;
-A Cone 10 Porcelain had a high MOR and was quite strong. (clay body had 0%
abs.)
-The same porcelain clay body with a crazed glaze on it had a marked
decreased MOR and was substantially weaker.
-A Cone 6 clay body with a proper fitting glaze was just as strong as a
cone 10 vitrified clay body.
Since a cone 6 clay can be vitrified equally as a cone 10 one can be. A
cone 6 clay body with a properly fitted glaze "is" stronger than a cone 10
clay body with a improperly fitted glaze.
-A crazed glaze weaken's the structural integrity.
I know you addressed your comments to Ron, and he is by far more
experienced to answer that question better. I just wanted to add my own
personal experience. The belief of whether having properly fitted glazes
or not is quite varied from person to person.
For myself I am aware that a crazed glaze will weaken the clay body, but I
love Shino's. Someone
else commented that some glazes have such a high expansion for the glaze to
have the proper effect. For example Chun blues required copious amounts of
calcium to get the iron to go that beautiful blue.
Personally I don't mind some crazed glazes but if was in full time
production making table ware I would make sure the glaze fit. Special ware
like serving platters I would not mind if I used a Shino that was crazed -
big deal.
It also doesn't bother me to see crazed table ware it's just I wouldn't
produced crazed table ware if I could help it.
Kat (in the Hat)
mudkat@telus.net
Ron Roy on wed 20 apr 05
I have never done any MOR experiments so I am greatful for Kat's comments
here. I makes sence to me that cone 6 clays can be every bit as servicable
as cone 10 bodies - if they are formulated properly.
Kat works for Plainsman Clays - and so does Tony Hansen. I know Tony has
been doing that kind of testing for years - and the fact is documented in
the industry literature - crazing weakens pots - you can take that to the
bank.
RR
>Des said:
>
>"...That said a non porous, non absorptive cone 11-12 body with a crazing
>glaze has to be much stronger than for example
>a non crazed one at cone 6 ;-) ..."
>Des
>
>That is a very interesting comment. Some time back I was involved in doing
>some MOR
>tests. (jeeps - that technician side of me is resurfacing.) The results
>were quite simple;
>
>-A Cone 10 Porcelain had a high MOR and was quite strong. (clay body had 0%
>abs.)
>-The same porcelain clay body with a crazed glaze on it had a marked
>decreased MOR and was substantially weaker.
>-A Cone 6 clay body with a proper fitting glaze was just as strong as a
>cone 10 vitrified clay body.
>Since a cone 6 clay can be vitrified equally as a cone 10 one can be. A
>cone 6 clay body with a properly fitted glaze "is" stronger than a cone 10
>clay body with a improperly fitted glaze.
>-A crazed glaze weaken's the structural integrity.
>
>I know you addressed your comments to Ron, and he is by far more
>experienced to answer that question better. I just wanted to add my own
>personal experience. The belief of whether having properly fitted glazes
>or not is quite varied from person to person.
>For myself I am aware that a crazed glaze will weaken the clay body, but I
>love Shino's. Someone
>else commented that some glazes have such a high expansion for the glaze to
>have the proper effect. For example Chun blues required copious amounts of
>calcium to get the iron to go that beautiful blue.
>Personally I don't mind some crazed glazes but if was in full time
>production making table ware I would make sure the glaze fit. Special ware
>like serving platters I would not mind if I used a Shino that was crazed -
>big deal.
>It also doesn't bother me to see crazed table ware it's just I wouldn't
>produced crazed table ware if I could help it.
>
>Kat (in the Hat)
>mudkat@telus.net
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jonathan Kaplan on wed 20 apr 05
Much of our work is at cone 6 and I would concur with Ron that cone 6
bodies are as strong as if not stronger then their counterparts at cone
9-10. I will ask a colleague of mine who has a great lab for clay
testing to MOR our clay body and we will see what data it can provide.
My clay bodies are formulated correctly from ratios between plastics
and non-plastics for each temperature range. I have developed these
ratios from years of experience making clay bodies for all types of
claywork...throwing, pressing, casting, etc. and they work.
I'll also agree with Ron on the crazing issue. Its funny too. We have a
project for a client making a line of lamp bases based on Asian
inspired forms. One of the requirements was that there be a crazed
surface. So I developed a line of transparant/translucent craze glazes
for cone 6. Very beautiful surfaces for decorative pieces indeed. I
would be loath to ever put them on an surface that comes into contact
with food or drink
Yes, I did all the formulation in Insight. Made it very easy.
Respectfully,
Jonathan
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139
(please use this address for all USPS deliveries)
Plant Location:
1280 13th Street Suite K
Steamboat Springs CO 80487
(please use this address for all UPS, courier, and common carrier
deliveries only!!)
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
Lee Love on thu 21 apr 05
Ron Roy wrote:
>Kat works for Plainsman Clays - and so does Tony Hansen. I know Tony has
>been doing that kind of testing for years - and the fact is documented in
>the industry literature - crazing weakens pots - you can take that to the
>bank.
>
>
In lower fire ware that is structurally weaker and not vitreous, crazing
is a more important strength factor.
Check out these "flawed" Ido teabowls. They are all over 400 years old.
( A way to get a simlilar look, without crazing, that I used to use, is
to use Rhodes crackle slip under Sander's Tamba. You get the crazed look
under the uncrazed glaze)
http://hankos.blogspot.com/
From the Japanese website:
/ 　Ido Jawan(Ido Chawan) was said to be the most inferior offering dish
in many kinds of Kourai Jawan . It was considered that Kairagi (the
shape of typical shark skin around the foot) of Ido Jawan was a failure
as its glaze did not melt well . However, in Japan, the simple vessel
was esteemed as a symbol of Wabi-Sabi (Taste for the simple and quiet).:/
--
Lee in Mashiko, Japan http://mashiko.org
http://hankos.blogspot.com/ Visual Bookmarks
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