Lili Krakowski on sun 26 aug 07
Bisquing is to pottery what parboiling is to cooking. Kinda. Not exactly.
Sort of.
Clay is full of materials that need to burn out. For one they WILL burn
out, as they disintegrate at temperatures well below that at which the clay
becomes a solid, long lasting
material. Hold on to that thought.
You write: ""Stoneware should be bisque fired between C/010 & up to C/06." I
thought
stoneware should be fired at Cone 4 and up?"
Well, stoneware IS glaze fired from c.4 up....but BISQUE fired at lower
temps. You are conflating your firings. Bisque is bisque.
Glaze-fire-whether glaze is used or not-is the second, final firing (as far
as the clay body is concerned. There may be further firings for luster and
similar additions to the glaze.)
You write: "I did my first glaze firing weeks ago, pieces were fired by
someone else
at Cone 4. I did my first bisque firing myself and was told that I
should fire Cone 6 Clay at Cone 6. The pieces came out a yellowy tan
color. Forgive my description, not sure how to describe it.
"But I do know that the Cone 4 bisque firing is more porous and pink, so
the glazes will come out 'brighter' then the Cone 6 bisque firing"
This confuses the heck out of me. I do not have any idea what this
represents. Someone told you to fire the c.6 clay to cone 6. Makes sense.
A size 6 shoe is made for a size 6 foot.
Then someone else fired your
pottery to c. 4 and the color was nicer than at c. 6.
Color of what? The clay body? The glazes?
I CAN understand is that either the clay or the glaze looked like what a
friend of mine used to describe as "baby's first Summer."
Bisque firing is done to a temperature well below the glaze firing, although
commercial china makers may reverse the order. But we are potters, not
china factories.
The CLAY will change color in the bisque and possibly be nicer looking at
this temperature than at that.
The color of the bisque does not matter. What the clay looks like at
maturity is what you should care about.
Clays that fire white at maturity may be ash gray after the bisque. Red
clays may be a stupid brown after bisque and a warm brick at maturity. So
stay focused on the "final" color.
How bright or nice the glazes, repeat, glazes, will look after the glaze
fire has little to do with the color of the clay after bisquing. A cone 6
glaze will not mature at c.06 and probably only begin maturing at c.1. Its
color may be gray, tan, whatever-it does not matter: what does is the color
of the glaze at maturing.
Why exactly do we bisque fire? We do NOT have to. Single-firing is a
time-honored method, the glaze is applied to the raw clay, and the whole
thing-raw clay, raw glaze fired together, only once.
Remember the thought I asked you to hold onto?
As the clay is heated materials will burn out. Before they do they
disintegrate and form gases. These gases need to "escape" from the pot and
will do so
with considerable force. The most frequently used example is a when a damp
pot is fired fast and the steam that is formed blows it to smithereens.
One reason then for bisque firing is to let these materials-turned-to-gas
burn out without disturbing the glaze coat. Another reason : that after the
bisque the pot still is porous but no longer will soften....so one can hold on
to it for glazing without fear that the pot will become misshapen or
dissolve!. Another reason is that many faults and defects in a pot will
show up through bisquing-cracks will open, warping warp, and so on. As raw
pots to be bisqued can be stacked one in each other, and a bisque kiln
REALLY crowded, one saves some money by bisquing, esp. when one is a
beginner who makes a good many pots that will not make it through the glaze
fire.
As to how to bisque fire. Dry the pots thoroughly. How long that takes
depends on the weather, how warm/cold the room is, how damp it is. A pot
may dry in a few hours, it may take a few days. How thick or thin the piece
is matters. It is much like clothes on a clothes line! Your diaphanous
nightie dries in minutes, the Turkish toweling bathmat takes a full day.
When the pots are dry, stack them in the bisque kiln. Some people use no
shelves at all, some use a few shelves...
We had a big go-around on bisquing a few weeks ago...I am a great believer in
firing bisque very very slowly. All I can give you is my electric kiln
schedule
I leave the lid propped up, and have all plugs out. I turn the bottom
element on low and leave the kiln that way overnight. In the morning I
close the lid. I then put the other elements on low and after an hour or
two-depending on how thick the pieces in kiln are--I turn all elements to
medium for two hours, then to high till the cone is reached. For sculpture I
may turn the kiln off in the morning, plug all but the top plug, leave it
till afternoon and restart in the order above. Yes, I generally fire bisque
with the plugs out. Many people put all plugs in except top one.
As to books. I will again and once more express my detestation for books
named " Whatever for Dummies".
There is nothing dummyesque about not knowing something one has not learned.
So go to the library and just load up on all the clay books there! Kenny,
Birks, Fraser, Rhodes...the list is huge.
Good luck.
Lili Krakowski
Be of good courage
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