Gretchen Zinkan on sun 11 nov 01
Thank you so much for your responses to my queries.
1. One of the challenges that I have is I have a skutt kiln with only low,
medium and high...so keeping track of what temperature I opened the kiln is
not easy and my pyrometer does not seem to be very accurate....so I have
debated buying a new kiln and saw one in ceramics monthly that looks like it
would do both reduction and raku. Does anyone have experience with this
type of kiln? The other possibility is to use this old kiln (that needs
some new bricks and elements) as a raku kiln...and buy a straight reduction
kiln. With a reduction kiln...I can do both oxidation and reduction
right??? Any and all discussion about this would be greatly appreciated.
2. In yesterdays clay art someone said that only those things fired to
vitrification point (high fire) are microwave reliable. Is this accurate?
I was under the belief that my ^6 stuff was ok in the microwave.
Gretchen Zinkan whose in British Columbia waiting patiently for her kiln to
cool
John Hesselberth on sun 11 nov 01
on 11/11/01 12:47 PM, Gretchen Zinkan at gzinkan@CYBERLINK.BC.CA wrote:
> 2. In yesterdays clay art someone said that only those things fired to
> vitrification point (high fire) are microwave reliable. Is this accurate?
> I was under the belief that my ^6 stuff was ok in the microwave.
Hi Gretchen,
If your cone 6 body is well vitrified then it should be OK in a microwave.
You can easily test this by measuring water absorption (should be less than
3% and preferably 1-2%). You can also test it directly in a microwave.
Check the archives for how to do this safely.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Snail Scott on mon 12 nov 01
At 10:47 AM 11/11/01 -0700, Gretchen wrote:
>...In yesterdays clay art someone said that only those things fired to
>vitrification point (high fire) are microwave reliable...
>I was under the belief that my ^6 stuff was ok in the microwave...
^6 is usually considered high-fire. The important factor is
absorption, though. A properly formulated ^6 body, fired to
^6, should have only about a percent or two of absorption. A
^10 body fired to only ^6 will have a much higher absorption,
for instance, even if it is OK at ^10. Test your clay to find
out its absorption, if you are curious, but if it's a well-
formulated ^6 clay fired to ^6, it's probably fine.
The problem with undervitrified clays is that their higher
absorption allows water (as from dishwashing) to penetrate
into the fired clay, and this moisture can explode into steam
when placed in a microwave. Glazed earthenware is especially
prone to this, since the moisture can get in through crazed
glazes and 'dry' feet, (ironic, no?) but has trouble escaping
again.
-Snail
Snail Scott on tue 13 nov 01
At 12:29 PM 11/13/01 -0500, you wrote:
>Snail, or anyone else
>
>I use a ^6-10 body and ^6 glazes. where does this put me on the
vitrification
>continuum?
Possibly a bit high in absorption, but it will depend
on the specific clay body. Test it yourself, under your
own normal firing conditions, to find out:
Make a test piece of clay, fire it, then weigh it.
Put the fired test piece in a pot of water and boil it.
Let the water cool, then remove the clay and wipe it dry.
Weigh it again. Convert the difference into a percentage.
(Take the 'wet' number, and subtract the 'dry' number
from it, then divide by the 'dry' number, and multiply
that answer by 100 to get the percentage.)
Example: 260 grams minus 250 grams equals 10 grams.
10 divided by 250 equals .04, so the absorption of
this test would be 4%.
-Snail
Millie on tue 13 nov 01
Snail, or anyone else
I use a ^6-10 body and ^6 glazes. where does this put me on the vitrification
continuum?
Millie in Sunny Md.
Snail Scott wrote:
>
>
> ^6 is usually considered high-fire. The important factor is
> absorption, though. A properly formulated ^6 body, fired to
> ^6, should have only about a percent or two of absorption. A
> ^10 body fired to only ^6 will have a much higher absorption,
> for instance, even if it is OK at ^10. Test your clay to find
> out its absorption, if you are curious, but if it's a well-
> formulated ^6 clay fired to ^6, it's probably fine.
Cindy Strnad on tue 13 nov 01
Dear Millie,
Your clay vitrifies at some point, probably
between ^6 and ^10. You can find instructions for
checking whether your clay is sufficiently
vitrified in the archives. No one can tell you
without doing these tests. If you subscribe to
Clay Times or have access to it, look through the
back issues. I did an article on microwave safety
that has this information in it--last year, I
think.
Best wishes,
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
vince pitelka on tue 13 nov 01
> I use a ^6-10 body and ^6 glazes. where does this put me on the
vitrification
> continuum?
Millie -
My own personal opinion is that it is improper and unethical to market a
cone 6-10 claybody for functional ware, because if the clay is appropriate
for cone 10, then at cone 6 it will be under-vitrified, and if it is
appropriate for cone 6, then at 10 it will be over-vitrified. I do not
believe that there is any such thing as a good functional-ware claybody
which can effectively cover such a wide firing range. Sorry to be so hard
on your claybody, but you need to know this.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Virgil and Susan Leise on wed 14 nov 01
Gretchen, I have a skutt kiln like the one you discribed....email me off
list and I would be glad to share my firing schedule with you!
Susan
vsleise@gpcom.net
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