Lili Krakowski on mon 7 feb 11
Holli: Let us take it one step at a time.
As I do not have a computer equipped kiln, you need to rely on someone =3D
else to tell you about whether the temp you have set your kiln to is =3D
right or not.
However. There is NO hard and fast rule for firing/overfiring. For =3D
instance many a matt glaze turns into a lovely transparent when =3D
"over-fired." Many a shiny glaze turns dull and matt at a slightly =3D
lower temp. The status of a glaze is quite elastic. The status of a =3D
clay depends on what degree of absorption the potter will tolerate, or =3D
wants.
So. To find out what the proper firing temp is for a clay you need to =3D
make tests. And these tests generally are tiles or bars. I make mine =
=3D
about 6 inches long, and 1.5 inches wide, and about 1/4 inch thick. I =3D
draw a line on them and mark the line at 10cms.
I then fire the bars to the "desired" temp. By measuring the line I can =
=3D
check shrinkage (very important). I then weigh the bars and boil them =3D
in water.. People disagree about how long to boil...I go with a good =3D
half hour...others boil longer. I remove the bars pat them dry on a =3D
towel--or shirt tail--and weigh them again. This will tell me how =3D
absorbent the clay is. =3D20
I try for 1 % no more than 1.5% absorption. So I know that if at c.5 =3D
--let us say--the bar absorbs 5% water it is underfired, and if it =3D
absorbs nothing it is overfired or close to it. (We are talking =3D
stoneware, not porcelain.)
So test your clay. If it is in the ball park it is not overfired.
As to your glazes. Duh. I do not know what "burnt through" means, not =3D
really. If the glaze is overfired it will have soaked into the pot more =
=3D
than it should,. If you spread butter on bread it stays on top. If you =
=3D
spread it on cooled toast some soaks in, some stays on top. If you put =3D
it on hot toast it all soaks in. If your glazes looks like butter on hot =
=3D
toast they probably are overfired.
Here the suggestion would be to make straight line blends and just up =3D
the clay content 3% or so at a time. =3D20
I do not see why your cone 6 should bend at all. It seems to me for a =3D
good c.5 the c6 cone would be straight but a bit shiny.
Suggestion: Put three cones in...a c4, c5. c6. As far as I know the c. =
=3D
4 should be molten, the c5 elegantly bent over, and the c.6 shiny but =3D
straight.
You WILL have to test...
Lili Krakowski
Be of good courage
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