Gillian Whittle on thu 6 may 04
For a while now I've been curious about the affect that refiring at =
bisque temperatures (i.e. ^06 - ^04) would have on the total heat work =
done on a pot made of, say ^6 clay. I know that refiring at maturity =
effectively means that the pot has reached a higher cone, but what about =
multiple firings at a lower temperature? And would cristabolite =
formation be an issue in structural integrity if you did do multiple =
refirings?
Thanks in advance!
Gillian Whittle
Hope Tree Pottery
St. John's, Newfoundland
Canada
Ron Roy on fri 7 may 04
Hi Gillian,
KNaO starts fluxing about 800C - so - yes there will be some additional
melting but it would not be very much.
It would make for an interesting experiment.
Glazes will melt more - even cone 10 glazes will start to soften again
above 800C to 900C.
Cristobalite is not produced until 1100C so that would not be a factor. If
there was already cristobalite present - it can be trouble on the way up if
you go too fast - same with the quartz. Normally there is not much - if any
- cristobalite in cone 6 bodies - certainly never in porcelain fluxed with
Neph Sy or spar.
RR
>For a while now I've been curious about the affect that refiring at bisque
>temperatures (i.e. ^06 - ^04) would have on the total heat work done on a
>pot made of, say ^6 clay. I know that refiring at maturity effectively
>means that the pot has reached a higher cone, but what about multiple
>firings at a lower temperature? And would cristabolite formation be an
>issue in structural integrity if you did do multiple refirings?
>
>Thanks in advance!
>Gillian Whittle
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Bobbruch1@AOL.COM on fri 7 may 04
Gillian Whittle
For a while now I've been curious about
the affect that refiring at
bisque temperatures
(i.e. ^06 - ^04) would have
on the total heat work done
on a pot made of, say ^6 clay.
I know that refiring at maturity
effectively means that the pot
has reached a higher cone,
but what about multiple firings
at a lower temperature?
And would cristabolite
formation be an issue
in structural integrity if you
did do multiple refirings?
I don't have the knowledge to
comment on the cristabolite
issue other than to say that
ANY refire requires a very slow
firing cycle, at least on the
upswing in temperature. Also,
I refire many pieces in cone 06
bisques because I find that putting
one glaze on and then rebisquing
is often the best way to layer glazes
for a cone 6 firing. I have never
found any structural problems firing
this way.
Bob Bruch
william schran on fri 7 may 04
Gillian wrote:> I know that refiring at maturity effectively means
that the pot has reached a higher cone, but what about multiple
firings at a lower temperature?<
My take is that refiring ware through the quartz inversion
temperatures, and especially those clay bodies with high formation of
cristabolite, may be subject, or more prone to cracking. I would
expect slow temperature rise and cooling through quartz inversion
would be preferable.
Bill
Carol Tripp on sun 9 may 04
Bob,
Would you mind elaborating on your method of glazing one layer, then bisque
firing again, then putting on more glaze? Do you do this with all glazes or
only certain ones? Why?
I'm not asking for any 'trade' secrets, just curious as to what's going on
and the reasons behind it. How did you come up with this method? (I know
that some people who have to transport their pots for a glaze firing, bisque
the glazed pot and then transport it but they do this just to protect the
surface.)
Thanks and best regards,
Carol
Dubai, UAE
>From: Bobbruch1@AOL.COM
>>I don't have the knowledge to
>comment on the cristabolite
>issue other than to say that
>ANY refire requires a very slow
>firing cycle, at least on the
>upswing in temperature. Also,
>I refire many pieces in cone 06
>bisques because I find that putting
>one glaze on and then rebisquing
>is often the best way to layer glazes
>for a cone 6 firing. I have never
>found any structural problems firing
>this way.
>
>
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Des & Jan Howard on sun 9 may 04
Carol
I don't want to pre-empt Bob, but any questions posed
on Clayart are "shotgun" queries so, here's my reply.
One of our celadon glazes needs a very, very thick coat so,
we glaze the biscuit pot as thickly as we dare, re biscuit fire
& glaze the pot thickly again, then into the glaze fire.
If you care to fire the kiln to cone 11, let cool to about 1050-1060C,
light the kiln again, & let it sit at this temp under strict
oxidation for about 4 hours the glaze develops a
translucency & texture that is delightful (luvya Hank!!, orright, Mel too).
Des
Carol Tripp wrote:
> Bob,
> Would you mind elaborating on your method of glazing one layer, then bisque
> firing again, then putting on more glaze? Do you do this with all glazes or
> only certain ones? Why?
>
> I'm not asking for any 'trade' secrets, just curious as to what's going on
> and the reasons behind it. How did you come up with this method?
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Gillian Whittle on sun 9 may 04
Hi Ron,
Thanks for your take on refiring bisque. I'm going to throw in one more
variable based on your response: what would happen if a low-fire glaze were
put on the piece after the first ^06 firing and then the piece was refired
over and over. Would that make a difference? I think I will try this but I
would like to know your thoughts on the subject (or anyone else's for that
matter!).
Thanks again,
Gillian Whittle
Hope Tree Pottery
St. John's, Newfoundland
Canada
Ron wrote:
>
> KNaO starts fluxing about 800C - so - yes there will be some additional
> melting but it would not be very much.
>
> It would make for an interesting experiment.
>
> Glazes will melt more - even cone 10 glazes will start to soften again
> above 800C to 900C.
>
Lee Love on mon 10 may 04
At the Orton site:
http://www.ortonceramic.com/Center/pdf_files/wall%20chart_degreeF.pdf
I found this information interesting about "bisquing cones for fast firing":
" If a cone is heated too fast, the cone
surface fuses and binders used to make
cones form gases that bloat the cone. If
cones are to be fired rapidly, they should
be calcined (pre-fired) before use.
Cones should be calcined to about 850°F
(455°C) in an air atmosphere."
I am assuming that Orton doesn't think the "pre-bisquing" effects
the final heat work.
--
in Mashiko, Japan http://mashiko.org
http://potters.blogspot.com/ Commentary On Pottery
Bobbruch1@AOL.COM on mon 10 may 04
Carol Tripp
Would you mind elaborating=20
on your method of glazing=20
one layer, then bisque
firing again, then putting=20
on more glaze?=A0 Do you=20
do this with all glazes or
only certain ones?=A0=A0Why?
First, I don't have a spray gun,
so I paint glazes on my pots.=20
I started by noticing a difference
between double layer glazes from
a bique state, and adding a second
layer to a piece that was already
fired to temperature. I had no
particular reason other than to see
what occurs in other applications.
Some glazes do OK with a painted=20
double glaze application on bisque
ware. For instance, certain solid=20
blue or green glazes that work well
under an ash glaze can be applied=20
this way, although you may get=20
slightly different results from the other=20
firing methods. I also don't know how=20
much of a factor clay bodies are to
this equation.
I have been trying to double layer various
whites - and I am finding that for certain
effects, an extra firing seems to produce
better - more even - results.
Caveat - try it on test tiles or on pieces that
you consider seconds, perhaps where there
is a glaze imperfection.
Also, I am often a pieceor two short for my
firings, so I don't mind an extra step. This might
not work as well for those with a different firing
schedule.
/////I'm not asking for any 'trade' secrets,=20
just curious as to what's going on
and the reasons behind it.=20
How did you come up with this method?=A0=20
No problem - no "trade secrets" involved....=20
just a trial and error method with no
scientific underpinnings.
Bob Bruch
Ron Roy on mon 10 may 04
Hi Gillian,
I should have said - the exception would be with any low fire bodies that
approached vitrification - or glazes.
One of the problems with low fire ceramics is the amount of flux needed to
melt clays and glazes. So much melter is needed that the firing range of
both clays and glazes is short.
So in the case of low fire glazes - at bisque temperatures - there will be
a lot more melting.
The reason low fired clays are usually not vitrified enough to prevent
leaking and moisture absorption is - when you add enough flux to make them
so - the firing range becomes so short that it is impossible to count on
the ware not being under or over fired. In other words the firing range
become too short.
Refiring the clay will not be much of a concern unless it is fluxed with a
frit - but the glazes will probably change dramatically - protect your
shelves!
It should be easy to track what happens to the bodies when they are refire
many times - just include a test bar and measure the absorbency after each
firing. If you need instructions on how to do the testing just let me know.
I would certainly be interested in seeing the data or a chart of the changes.
The result could be - making a clay body that would have the right amount
of vitrification after several refirings. It would also be possible to
construct glazes that would act in the same way.
Using refiring to promote crystal development will not work if the glaze is
taken to it's original top temperature. That would remelt the crystals and
they would have to start to reform again. The seeding material might also
get melted with would result on the crystals taking a longer time to reform
- if at all.
Wish I had a clearer idea about what you are trying to do - I don't know if
I'm even answering the right questions.
RR
>Hi Ron,
>Thanks for your take on refiring bisque. I'm going to throw in one more
>variable based on your response: what would happen if a low-fire glaze were
>put on the piece after the first ^06 firing and then the piece was refired
>over and over. Would that make a difference? I think I will try this but I
>would like to know your thoughts on the subject (or anyone else's for that
>matter!).
>
>Thanks again,
>
>Gillian Whittle
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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