iandol on fri 30 may 03
Dear Butch Welch,=20
Both styles of firing program are valid. Results from a protracted =
cooling cycle are sometimes called Continuous Cooling Transformations. =
Those gained by quench cooling and reheating with a dwell period to =
allow the changes to take place are called Isothermal Transformation.
These terms are not commonly used in Studio Ceramic Circles but they are =
frequently employed in the metal trades.
It is most probable that each would give differing results with the same =
glaze.
One point to bear in mind is the Glass Transition, the temperature at =
which a glass or glaze commences to soften. Though we may have fired our =
glaze at a very high temperature, it will begin to soften at a much =
lower temperature depending on the Alkali Metal content (K2O/Na2O). This =
can be as low as 600 Celsius. As the temp goes up crystals can nucleate =
and grow.
Only testing will reveal the potential of any glaze but it is probable =
that those that contain Magnesia and or Calcia will respond well.
Best regards,
Ivor Lewis. Redhill, South Australia
Brenda Anderson on sat 31 may 03
I did my first test on crystals yesterday in my Skutt 1027 (new) and boy
did, the studio get HOT. I did it in 6 segments as my instructor had told
me. The glaze is beautiful but no crystals. Any thoughts??
Daughter of Clay
Brenda
----- Original Message -----
From: "iandol"
To:
Sent: Friday, May 30, 2003 2:02 AM
Subject: Kiln Slow cool down Vs Refire
Dear Butch Welch,
Both styles of firing program are valid. Results from a protracted cooling
cycle are sometimes called Continuous Cooling Transformations. Those gained
by quench cooling and reheating with a dwell period to allow the changes to
take place are called Isothermal Transformation.
These terms are not commonly used in Studio Ceramic Circles but they are
frequently employed in the metal trades.
It is most probable that each would give differing results with the same
glaze.
One point to bear in mind is the Glass Transition, the temperature at which
a glass or glaze commences to soften. Though we may have fired our glaze at
a very high temperature, it will begin to soften at a much lower temperature
depending on the Alkali Metal content (K2O/Na2O). This can be as low as 600
Celsius. As the temp goes up crystals can nucleate and grow.
Only testing will reveal the potential of any glaze but it is probable that
those that contain Magnesia and or Calcia will respond well.
Best regards,
Ivor Lewis. Redhill, South Australia
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
william schran on sun 1 jun 03
Brenda wrote: 1027 (new) and boy
did, the studio get HOT. I did it in 6 segments as my instructor had told
me. The glaze is beautiful but no crystals. Any thoughts??>
Did you use witness cones through out the kiln so that you would have
a more accurate reading of the firing temperature? I find these
records of my crystalline firing extremely valuable when I want to
repeat results.
Are your results a smooth, glossy, semi-transparent glaze? May have
fired too high for this particular glaze, taken too long for the last
100 degrees of temperature rise or may be the holding temperature is
too high. Any number of factors can contribute to crystal formation -
or not. Suggest you stick with one glaze and fiddle with firing and
holding temperatures.
Bill
| |
|
