Christopher Anton on sat 14 oct 00
----- Original Message -----
From: "Jonathan Kaplan"
>
> The first is that it be high enough to take care of the LOI. This is...
>The point being that pinholing at that temperature is a
> direct result of improperly burned out LOI.
Ok, I'm still a relative neophyte, I'll ask. What is "LOI?" Loathsome
Optional Insects?? : )
- Chris (Who really does want to know!)
Jonathan Kaplan on sat 14 oct 00
Yes I agree that bisque temperatures are indeed a personal thing. What
works for me may not work for you and its important that we all have our
individual preferences and interpretations regarding pottery dogma.
However, there are some things to consider about bisque temperature no
matter what cone you bisque to.
The first is that it be high enough to take care of the LOI. This is
especially true of earthenware clay bodies and terra cotta clay bodies in
the 06-04 range. I've written extensively about this on the list and in
other publications. The point being that pinholing at that temperature is a
direct result of improperly burned out LOI. I've worked with perhaps as
many majolica glazes that we have in our notebooks and its not the glaze,
its the LOI from the ball clays and the red clays that are problematic.
Burn it out, no pinholing. Bisque too high, the body tightens up too much
and yo can get enough glaze on the surface worth a damn.
Secondly, too low a bisque will cause the ware to crack when it is dipped
into the glaze as the water absorbed into the clay structure expands the
overly porous body and it developes a fine network of cracks that will be
realized in the glaze firing. Avoid weak bisque by taking it high enough.
The change from kaolinite to metakaolin at 600 degrees C produces ware that
can be called bisque but depending on the clay body, the bisque temperature
is usually higher and needs to be so to take care of the LOI as well as
create enough structural bonding in the clay body so as not to be affected
by the infiltration of water and the resulting expansion issues. (yes
that's a run on sentence, I know!) If you have a questionable clay body or
your clay manufacturer doesn't have a clue, perhaps some dillitometric
tests might be encouraged.
There is a range of temperatures that work for bisque firing. It depends on
the clay body formula and what you feel works for you and produces the
results you need.
In our plant, all work with the exception of low temperature earthenware
gets bisque fired to cone 06. The earthenwares get bisque fired to cone
04. Our mid range terra cotta (cone 3-4) also gets a cone 06 bisque. We
have virtually eliminated any OM 4 ball clay as it is a nasty culprit full
of all kinds of garbage in all our clay bodies. Our casting bodies use FC
340 and we are moving our plasic bodies to Tennesse #5 or #10 when
possible. We are also using alot of Starcast Ball Clay in our plastic
bodies as it too is a very clean ball clay.
Jonathan
Jonathan Kaplan
Ceramic Design GroupLTD/Production Services
PO Box 775112
Steamboat Springs, CO 80477
(970) 879-9139 voice and fax
http://www.sni.net/ceramicdesign
UPS: 1280 13th St. Unit13
Steamboat Springs, CO 80487
Jonathan Kaplan on sun 15 oct 00
>----- Original Message -----
>From: "Jonathan Kaplan"
>
>>
>> The first is that it be high enough to take care of the LOI. This is...
>>The point being that pinholing at that temperature is a
>> direct result of improperly burned out LOI.
>
>Ok, I'm still a relative neophyte, I'll ask. What is "LOI?" Loathsome
>Optional Insects?? : )
Loss On Ignition.......
The burning out of carbonaceous materials, the offending stuff in clay in
the early stages of firing.
Jonathan
Jonathan Kaplan
Ceramic Design GroupLTD/Production Services
PO Box 775112
Steamboat Springs, CO 80477
(970) 879-9139 voice and fax
http://www.sni.net/ceramicdesign
UPS: 1280 13th St. Unit13
Steamboat Springs, CO 80487
Diane G. Echlin on sun 15 oct 00
> Ok, I'm still a relative neophyte, I'll ask. What is "LOI?" Loathsome
> Optional Insects?? : )
>
> - Chris (Who really does want to know!)
Hey, I know the answer! (Waves hand in the air) pick me pick me!
LOI is Loss On Ignition, it's all the stuff that burns out like the water and
anything carbonaceous. If it isn't completely burned out during the bique it will
affect the quality of your glaze surface.
Clayart makes ya smart!
Diane in CT
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