Khaimraj Seepersad on sat 8 may 99
Dean and Nikom ,
I thought I might add on , that plastic clays [ montmorillionites ] can be
used if the
grog is raised to 80 0r 70 % . I use the stickiest , most swelling clays I
can find .
8 to 10 % pure Bentonite can be used as well , but the 90 % grog must be
mixtures of -200 mesh , - 300 mesh and beyond . Dries rapidly .
The grog is at - 200 mesh and can be fired clay [ over 950 deg . c. ] or
ground
cullet , also at - 200 mesh . The body is very plastic , but please note I
am
handbuilding on a Banding Wheel , turned rapidly by hand .
I fire small objects in a 6 x 6 x 4 [ high ] inch kiln , electric
, so there is a
good deal of radiant heat bouncing around - throws the pyro off by 50 to
100 deg. c. I hit 1280 in about 2 or 3 hours , or less if the coils are
weakening .
Usually the objects are less than 5 mm thick .
My clay grog is a naturally fired Porcellinite [ fires in the earth , from
gas / oil /
coal ] just has to be sifted .
From - Khaimraj Seepersad [ Caribbean ]
-----Original Message-----
From: nikom chimnok
To: CLAYART@LSV.UKY.EDU
Date: 07 May 1999 8:47
Subject: Re: FAST FIRING-The Need for Speed
----------------------------Original message----------------------------
Hello Dean,
I figured Clayart would explode with responses to your queries, so I
didn't bother to respond the first day. But nobody answered, so I'll tell
you what I know.
First, how fast you can fire has most to do with your claybody. You
can design a clay which will fire fast, but you might be stuck with one
which will only fire slow. Several materials are the friends of the fast
firer: talc, wollastonite, grog, and kaolin. The enemies are ball clay and
very plastic red clays. Small particles sizes promote plasticity, and at the
same time allow water to migrate out of the pot slowly. Large particle size
and inert ingredients allow fast water migration and fast firing. I've seen
the clay formula for a local company that fires tiles in a continuous kiln,
from room temperature to 1200 degrees C to cool in one hour. The tiles are
pressed and contain very little clay.
The first danger of fast firing is explosion. If the water in the
clay boils and the steam can't escape, the pot will explode. Grog is the
best insurance against explosion. The second danger is cracking. Here's
where talc and wollastonite help.
The clay mix is extremely important. Our local clay is normally
once-fired for two days and cooled for two, and still explodes and cracks
50% and more. But with 60% local clay plus additions of ingredients
mentioned above, I can once-fire it with 100% success in 6 hours--that's
from the time of lighting the fire to cone 04. No candling.
Thickness is also important. The thicker it gets, the longer you
have to fire. This is easy to understand--it's the same problem of the
turkey being burnt on the outside but raw inside. With clay the result is
not inedibility, but explosions and cracking.
As to Fred Olsen's fast firing, I think he is not generally talking
about bisque. It's a pretty unusual claybody you can bisque in 4 hours. The
only time I've fired an Olsen kiln was in college, where we bisqued in an
electric kiln for about 12 hours, then glazed with wood in 6. It's much
easier to do a fast glaze firing than a fast bisque firing, because you
don't have the water to contend with. I'm not commenting here on the quality
of the glaze, only the possibility of breaking the pot.
At present we once-fire glazed pots about the size you're talking
about to 1230 C in around 16 hours. The clay contains 20% grog, and never
explodes. We start it slow, proceed at 50 degrees C per hour to 650, then
put the pedal to the metal and finish as fast as the kiln will go. Above
650, a rise of 300 degees per hour doesn't hurt a thing. We do get the odd
crack, but it is considered cheaper to put up with this than to buy the
ingredients to stop it.
I hope this discussion is helpful to you.
Regards,
Nikom, in Thailand, where the mangoes are now so plentiful they're
practically giving them away.
****************************************************************************
******
At 14:06 4/5/99 EDT, you wrote:
>----------------------------Original message----------------------------
(snip)
>Until now I haven't had a kiln that could fire really fast. Now I can see
>the possibility of going from 300F to 2250F in about four hours. Since I've
>never fired this fast I'm wondering if it's wise to risk a kiln load of
pots
>to find out if it can be done.
(snip)
Bisqueing might be a factor, too. In
>'The Kiln Book' Fred Olsen describes fast firing his wood kiln from
>400-2300F in 4 hours but he's probably firing bisque..
(snip)
>How fast can you go? How fast do you go? I'd like to hear from anybody
that
>has explored high speed firing. What are the dangers? What are the
>parameters?
>
>Dean in Beautiful, Expensive Kauai
>
>
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