mariko cruse on fri 3 aug 01
Hello Clayarters,
I have a question to ask. When a clay supplier sells a claybody, which =
has a cone range from 6 to 11, and the ave. absorption is less than l% =
at both low and high end of the cone range as described in their =
catalog, what are the deciding factors in choosing the cone? Is it =
possible to have a same absorption at such a wide temp. range?
I fired a test tile, which is made from this claybody(porcelain), to =
Cone 9 in a gas reduction kiln, and the tile bent almost to 2 o'clock =
position, while at Cone 6 the tile remained straight up. Would someone =
please explain this phenomenon and pros and cons of using this kind of =
claybody? Thank you in advance for your guidance. Mariko=20
David Hendley on sun 5 aug 01
It is pretty much impossible for a claybody to have a 1% absorption rate
at both cone 6 and cone 11, and be suitable for use at both extremes.
Clay manufacturers like say that their claybodies have a wide firing range,
but your test tile results show that there is a big difference. Trust your
tests.
Your best course of action is to fire some test bars at the temperature
you want to work at, and test them for absorption to see if the clay is
suitable
at that temperature.
With porcelain, you want an absorption of less than 1%, but you also need to
test for over-firing, which will cause excessive slumping, as evidenced by
the
bending of your test tile at cone 9.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "mariko cruse"
To:
Sent: Friday, August 03, 2001 9:40 PM
Subject: Cone rages of Clay bodies
Hello Clayarters,
I have a question to ask. When a clay supplier sells a claybody, which has
a cone range from 6 to 11, and the ave. absorption is less than l% at both
low and high end of the cone range as described in their catalog, what are
the deciding factors in choosing the cone? Is it possible to have a same
absorption at such a wide temp. range?
I fired a test tile, which is made from this claybody(porcelain), to Cone 9
in a gas reduction kiln, and the tile bent almost to 2 o'clock position,
while at Cone 6 the tile remained straight up. Would someone please
explain this phenomenon and pros and cons of using this kind of claybody?
Thank you in advance for your guidance. Mariko
Ron Roy on mon 6 aug 01
It is impossible to have any clay vitrify any where near the same amount
over the range of 5 cones.
Either it melts properly at the lower cone and is overfired above that or
its too open at the lower cone to be just right at the upper cone.
More heat means more melting - you cannot get around that.
It is hard enough to keep clay bodies vitrified the same amount at one cone
- never mind a range of 5 cones.
I'm willing to bet that clay company does no testing of their bodies - I
can just imagine what that body looks like at cone 11 if it's soft at cone
9.
The only way to deal with this kind of thing is to fire the body at
different temperatures and measure the absorption and decide if it's right
for what you want.
RR
>I have a question to ask. When a clay supplier sells a claybody, which
>has a cone range from 6 to 11, and the ave. absorption is less than l% at
>both low and high end of the cone range as described in their catalog,
>what are the deciding factors in choosing the cone? Is it possible to
>have a same absorption at such a wide temp. range?
>I fired a test tile, which is made from this claybody(porcelain), to Cone
>9 in a gas reduction kiln, and the tile bent almost to 2 o'clock position,
>while at Cone 6 the tile remained straight up. Would someone please
>explain this phenomenon and pros and cons of using this kind of claybody?
>Thank you in advance for your guidance. Mariko
>
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Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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