Michelle McCurdy on sat 6 jun 98
Hello. I know this has been discussed before but I'm having trouble finding it
in the archives. I have some students that have done pit firing but without
bisqueing. They have trouble with breakage. I suggested a low bisque like
^012. They are afraid they will loose the burnished surface. I was hoping
someone could answer this for me. I have very little experience with pit
firing but would like to help them find a better way.Thanks for any help!
Michelle
Marcia Selsor on sun 7 jun 98
^012 is correct for bisque temp. without losing the burnished surface.
Marcia in Montana
Michelle McCurdy wrote:
>
> ----------------------------Original message----------------------------
> Hello. I know this has been discussed before but I'm having trouble finding it
> in the archives. I have some students that have done pit firing but without
> bisqueing. They have trouble with breakage. I suggested a low bisque like
> ^012. They are afraid they will loose the burnished surface. I was hoping
> someone could answer this for me. I have very little experience with pit
> firing but would like to help them find a better way.Thanks for any help!
> Michelle
Grace Epstein on sun 7 jun 98
hi Michelle...012 is the bisque temp we fire all our "primitive" fired pieces
( raku, burnished & polished terra sig, sawdust and saggar ) We do not loose
the shine in the sawdust or saggar firings. you should be ok
Grace in sunny yet refreshingly chilly CT.(..great rowing weather...anyone out
there row as in crew )
Grace
Dannon Rhudy on sun 7 jun 98
They should bisque the wares first. Most do so. The bisque
range can run from as low as 018 up to cone 1. I usually go to
010; let them experiment a bit. The surface sheen will be
altered slightly, but they won't "lose their burnish".
----------------------------Original
message----------------------------
Hello. I know this has been discussed before but I'm having
trouble finding it
in the archives. I have some students that have done pit firing
but without
bisqueing. They have trouble with breakage. I suggested a low
bisque like
^012. They are afraid they will loose the burnished surface. I was
hoping
someone could answer this for me. I have very little experience
with pit
firing but would like to help them find a better way.Thanks for
any help!
Michelle
Bob Hollis on sun 7 jun 98
Michelle,
I know from experience that you can bisque burnished pots to
cone 08 and the surface will remain shiny,but you may lose any/all colour
from metallic salts etc.,cone 018 is better no matter which clay you use.My
personal choice is for pots that are not burnished.
Bob Hollis
Vince Pitelka on sun 7 jun 98
>Hello. I know this has been discussed before but I'm having trouble finding it
>in the archives. I have some students that have done pit firing but without
>bisqueing. They have trouble with breakage. I suggested a low bisque like
>^012. They are afraid they will loose the burnished surface. I was hoping
>someone could answer this for me. I have very little experience with pit
>firing but would like to help them find a better way.Thanks for any help!
Michelle -
Your suggestion is correct, although ^012 is pushing it a bit. I do a ^018
bisque on all burnished wares, and have no loss of shine, and no breakage in
the bonfire.
Good luck -
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Christopher J. Anton on sun 7 jun 98
>I have some students that have done pit firing but without
>bisqueing. They have trouble with breakage. I suggested a low bisque like
>^012. They are afraid they will loose the burnished surface. I was hoping
>someone could answer this for me. I have very little experience with pit
>firing but would like to help them find a better way.Thanks for any help!
I have bisque fired burnished stoneware to ^05 without significant loss of
the surface texture. I also have been able to retain most of the look on
burnished and bisqued ware by applying and buffing several coats of terra
sigilatta (sp?) and raku firing the items. I would expect similar results
from pit firing.
- Chris Anton
antons@bellsouth.net
Vince Pitelka on mon 8 jun 98
>I have bisque fired burnished stoneware to ^05 without significant loss of
>the surface texture. I also have been able to retain most of the look on
>burnished and bisqued ware by applying and buffing several coats of terra
>sigilatta (sp?) and raku firing the items. I would expect similar results
>from pit firing.
I am a little baffled by posts which say it is OK to bisque burnished wares
to ^08 or ^05 or ^1. I suppose some of it depends on the claybody beneath
the burnish, but when firing to normal bisque temperatures or above, there
is going to be some slight amount of shrinkage in the clay. If you have a
true burnished surface on top, it is so dense that it cannot shrink at all
without wrinkling on a microscopic level, diminishing or destroying the burnish.
Perhaps part of the problem here is a confusion between polishing and
burnishing. We have been through this lots of times before on Clayart, but
let me review the difference. Polishing involves rubbing with a soft cloth
or chamois or brush to create a shine on the surface, usually with a terra
sigillata coating. A polished piece is not particularly dense, and can be
bisqued to ^08 or ^06 with no loss of shine. A burnished surface, as the
term is used in many media areas other than clay, involves rubbing the
surface with a very hard smooth object. In the case of hard-leather-hard
clay, this compresses the surface to a great degree, eliminating air spaces
between particles, and lining up the platelates on the surface, creating a
dense shine.
Another factor is the degree of burnish. If you are just burnishing
lightly, to give a dull sheen, then the surface is not compressed very much,
and the piece will likely stand up to a ^08 bisque with little or no loss of
shine. But if you are doing a thorough burnish, ending up with a hard,
smooth, glassy shine, then bisqueing even to ^010 can reduce the shine, and
biqueing to ^08 or above will completely ruin it. Remember, a truly
burnished surface cannot shrink, so if the clay beneath it shrinks AT ALL,
it will wrinkle the surface and diminish or destroy the shine.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
John H. Rodgers on mon 8 jun 98
-- [ From: John H. Rodgers * EMC.Ver #2.5.02 ] --
HI! It's an easy thing to simply make two or three test peices, run a test
firing for bisque to 012 and see what happens. That is the proof. It will
show whether the 012 fire will cause loss of the burnished surface or not.
That way everyone will know absolutely what to expect. There is nothing like
a test to prove or disprove ones theory
Just a suggestion.
John Rodgers
-------- REPLY, Original message follows --------
Date: Saturday, 06-Jun-98 10:15 AM
From: Mmpottery \ America On-Line: (Mmpottery)
To: Multiple recipients of list CLAYART \ Internet: (clayart@lsv.uky.
edu)
Subject: low bisque for pit firing
----------------------------Original message----------------------------
Hello. I know this has been discussed before but I'm having trouble finding
it in the archives. I have some students that have done pit firing but
without bisqueing. They have trouble with breakage. I suggested a low bisque
like ^012. They are afraid they will loose the burnished surface. I was
hoping someone could answer this for me. I have very little experience with
pit firing but would like to help them find a better way.Thanks for any help
! Michelle
-------- REPLY, End of original message --------
Bob Hollis on tue 9 jun 98
Dear Vince,
What a load of crap,we have spent many hours burnishing
pots and bisque fired them as high as cone 08 and lost none of the surface
quality[we use stones and then glass to burnish]. When my results are the
opposite of what the scientist/technologist says will happen I do not stand
looking up at the eastern sky expecting to see an extra bright star,I take
what I get and admire.
Bob Hollis
Holly Velsor on tue 9 jun 98
Vince, in theory I agree with your statement about losing a good burnish
when bisque firing---but I have experienced some great burnished shines
after bisquing to ^O8 and ^06...not just from buffed terrasig.
I feel the guideline should be--Don't bisque any higher than ^08 but
that everyone should experiment with their clay body and see what
happens. But the bottom line with pit firing is: BISQUE FIRE FIRST or
you'll hear what sounds like popcorn under the coals!
Holly
>I have bisque fired burnished stoneware to ^05 without significant loss
of
>the surface texture. I also have been able to retain most of the look
on
>burnished and bisqued ware by applying and buffing several coats of
terra
>sigilatta (sp?) and raku firing the items. I would expect similar
results
>from pit firing.
I am a little baffled by posts which say it is OK to bisque burnished
wares
to ^08 or ^05 or ^1. I suppose some of it depends on the claybody
beneath
the burnish, but when firing to normal bisque temperatures or above,
there
is going to be some slight amount of shrinkage in the clay. If you have
a
true burnished surface on top, it is so dense that it cannot shrink at
all
without wrinkling on a microscopic level, diminishing or destroying the
burnish.
Perhaps part of the problem here is a confusion between polishing and
burnishing. We have been through this lots of times before on Clayart,
but
let me review the difference. Polishing involves rubbing with a soft
cloth
or chamois or brush to create a shine on the surface, usually with a
terra
sigillata coating. A polished piece is not particularly dense, and can
be
bisqued to ^08 or ^06 with no loss of shine. A burnished surface, as
the
term is used in many media areas other than clay, involves rubbing the
surface with a very hard smooth object. In the case of
hard-leather-hard
clay, this compresses the surface to a great degree, eliminating air
spaces
between particles, and lining up the platelates on the surface, creating
a
dense shine.
Another factor is the degree of burnish. If you are just burnishing
lightly, to give a dull sheen, then the surface is not compressed very
much,
and the piece will likely stand up to a ^08 bisque with little or no
loss of
shine. But if you are doing a thorough burnish, ending up with a hard,
smooth, glassy shine, then bisqueing even to ^010 can reduce the shine,
and
biqueing to ^08 or above will completely ruin it. Remember, a truly
burnished surface cannot shrink, so if the clay beneath it shrinks AT
ALL,
it will wrinkle the surface and diminish or destroy the shine.
- Vince
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Vince Pitelka on wed 10 jun 98
>Dear Vince,
> What a load of crap,we have spent many hours burnishing
>pots and bisque fired them as high as cone 08 and lost none of the surface
>quality[we use stones and then glass to burnish]. When my results are the
>opposite of what the scientist/technologist says will happen I do not stand
>looking up at the eastern sky expecting to see an extra bright star,I take
>what I get and admire.
> Bob Hollis
Bob -
Disregarding your unnecessarily rude language, as I mentioned in my post,
other's experience may well depend on the clay body used. If you are using
a very refractory body, and burnishing the clay itself rather than a slip or
terra sig coating, it is possible that you do not experience any shrinkage
in the bisque-fire, and your burnished surface remains intact. I am curious
how high a shine you achieve and if this shine is truly 100% preserved after
the bisque-firing. We often go for a shine that is almost like glass, and I
have never been able to preserve this shine when bisque-firing the pieces to
normal bisque temperatures. I cannot tell you the number of times my
students have laboriously burnished a surface (on many different kinds of
clay and many different kinds of slip or terra sig surfaces), and had the
piece accidentally placed in a normal ^08 bisque. In those cases, the
burnish has ALWAYS been ruined. That is the practical experience I have to
go on. Through thirteen years of teaching ceramics, including MANY Ancient
Clay workshops, it has universally been my experience that if I bisque-fire
burnished wares to normal bisque temperatures, the burnishing is ruined.
Glad to hear that your experience has been otherwise.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Bob Hollis&Hulda Dee on thu 11 jun 98
Dear Vince,
We use a marl which is dug from a clay seam on a
farm then put through a deairing pugmill.This clay still has
all the [impurities?]trace metals and will start to deform
at cone 04 and will become a shapeless mass at cone02.I
still do not believe all your technical jargon
[crap],remember science has proved that it is not possible
for the bumble-bee to fly,but that
damned,uneducated,contrary old bee just will not listen.
regards,
Bob Hollis
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