Opinion - Bisque Firing Cone 06 or 04

We have always bisque fired to cone 06. One of the potters has suggested
firing to cone 04 to help eliminate various glaze problems. Any opinions on
this?

Not sure what glaze problems you were experiencing, but for most of my
stuff 06 has worked fine. I used to bisque at 04 until one time I
think I over-fired a little and the clay lost so much of its porosity
that it was difficult getting glaze to adhere to it; that's why I only
go to 06 now and it is fine for my high fire and raku.

Two exceptions come to mind. Some teachers I've known (like my high
school teacher) bisqure students' pots at 04 so that it is less
vulnerable to breakage while glazing. Another exception is low-fire
ware. If you look at the label of many commercial low-fire glazes they
say to bisque at 04, even though the subsequent glaze-fire is only to
05 or 06.

"Eric" wrote in message
oups.com...
Not sure what glaze problems you were experiencing, but for most of my
stuff 06 has worked fine. I used to bisque at 04 until one time I
think I over-fired a little and the clay lost so much of its porosity
that it was difficult getting glaze to adhere to it; that's why I only
go to 06 now and it is fine for my high fire and raku.

Two exceptions come to mind. Some teachers I've known (like my high
school teacher) bisqure students' pots at 04 so that it is less
vulnerable to breakage while glazing. Another exception is low-fire
ware. If you look at the label of many commercial low-fire glazes they
say to bisque at 04, even though the subsequent glaze-fire is only to
05 or 06.

We were getting bubbling in a Gerstley based glazed (Erin's base) that had
been acting fine. I suspect that the Gerstley is changing with each order.
One potter suggested that we try firing at a higher bisque. The studio is
meant for students at the University and they have little or no experience
so I was not sure if the decreased porousity would be harder or easier on
them. It is interesting to hear that the higher bisque can benefit them.

We have actually been trying to replace our glazes that have Gerstley which
is what I think is probably the issue.

//************************************************** *********

Erin's White - BaseHM = 35
Bentonite 100
Gerstley B 3200
Flint 3000
Talc 2000
Soda Spar F4 1400
EPK (Kaolin) 500

10100
Green
Copper Carb 200

"DKat" wrote in message
...
We have always bisque fired to cone 06. One of the potters has suggested
firing to cone 04 to help eliminate various glaze problems. Any opinions
on
this?

[We were having pinholing problems in low-fire ware (not just Gerstly Borate
glazes). Firing the bisque to a maturity as high or higher than the glaze
helped eliminate the holes. I think these clays contain something volatile
that outgasses at peak temperatures, and makes its way out through the
molten glaze. On the other hand, the body was marginally less absorbant of
glaze, if that's an issue.]

Andrew Werby
www.computersculpture.com

"DKat" wrote in message ...
We have always bisque fired to cone 06. One of the potters has suggested
firing to cone 04 to help eliminate various glaze problems. Any opinions on
this?

04 fires it to maturity (or should if your kiln reaches the proper
temp.) for best results the bisque firing should be done 2 cones
higher than the glaze firing. the extra time and cost is minimal but
the result is a whole lot better, eliminating some of the blips that
can happen otherwise.

Jedi wrote:

We were getting bubbling in a Gerstley based glazed (Erin's base)
that had
been acting fine. I suspect that the Gerstley is changing with each
order.
One potter suggested that we try firing at a higher bisque. The
studio is
meant for students at the University and they have little or no
experience
so I was not sure if the decreased porousity would be harder or
easier on
them. It is interesting to hear that the higher bisque can benefit
them.

We have actually been trying to replace our glazes that have Gerstley
which
is what I think is probably the issue.

//************************************************** *********

Ah ha! Gertley Borate (aka "colemanite" I think?) I've been hearing
for a few years to start watching out for inconsistent gerstley coming
from the mine, which I think is somewhere in California. I continued
using it with no bad results so I started thinking it might be a "Paul
is dead" sorta thing. I guess they were right, whoever "they" are.
I'll bet you are right in thinking its the gerstley. But I am no glaze
chemist.
BTW -- the 06 bisqueware that took the gerstley fine often had a glaze
on it that was almost all gerstley: the 80/20 clear crackle raku glaze
that you see everywhere.

Good luck!

Eric
SpunMud

P.S.: by the way, when i mentioned that some people i know have
bisqued students' pottery a little higher, to cone 04, in order to
reduce breakage during "glazing," i just meant the process where the
bisqueware is touched, decorated, dipped and generally handled during
the glazing process -- not the glaze firing itself. the higher bisque
fire results in a more stout piece of ware that can better withstand
"rough" handling. sorry for being a bit vague there.

"Eric" wrote in message
oups.com...
P.S.: by the way, when i mentioned that some people i know have
bisqued students' pottery a little higher, to cone 04, in order to
reduce breakage during "glazing," i just meant the process where the
bisqueware is touched, decorated, dipped and generally handled during
the glazing process -- not the glaze firing itself. the higher bisque
fire results in a more stout piece of ware that can better withstand
"rough" handling. sorry for being a bit vague there.

I thought that was pretty clear. We have on occasion had the kiln
underfired due to error and had a lot of breakage because the person
unloading did not know the difference or didn't care. A sore point with me
since I feel protective of the students.

On 8 Feb 2005 13:43:36 -0800,
(walamalacalucy) wrote:

"DKat" wrote in message ...
We have always bisque fired to cone 06. One of the potters has suggested
firing to cone 04 to help eliminate various glaze problems. Any opinions on
this?

04 fires it to maturity (or should if your kiln reaches the proper
temp.) for best results the bisque firing should be done 2 cones
higher than the glaze firing. the extra time and cost is minimal but
the result is a whole lot better, eliminating some of the blips that
can happen otherwise.

If it wasn't obvious to all, note that the above rule of thumb assumes
that you are working with low-fire clay and glazes. The body maturity
(such as it is) comes entirely from the bisque firing. With
higher-fire systems (cone 6 and up, say) the bisque firing is simply
to give the piece enough strength to allow handling during
glazing, since the maturity of both body and glaze come in the
glaze firing. Some folks bisque lower (06 or even 08) to save on
energy, while others bisque to 04 to help get over as much out-gassing
from the body as possible to avoid bubbles in the subsequent glaze.
But of course with some glaze materials, the glaze itself can cause
bubbles. I think Gerstley is one of those.

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

I agree Particularly for Earthenware
"DKat" wrote in message
...
We have always bisque fired to cone 06. One of the potters has suggested
firing to cone 04 to help eliminate various glaze problems. Any opinions
on
this?