Des & Jan Howard on thu 15 jul 04
Hank
We have tried the lengthy oxidation soak at ~1050oC
on the way down from a Cone 11 firing with excellent results
on red shino, magnesia & celadon glazes.
Question.
Have you or anyone on Clayart tried taking pots previously fired
to say Cone 11 & refiring up to ~1050oC for a lengthy oxidation soak?
Des
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Hank Murrow on thu 15 jul 04
Dear Des;
Yes, I have re-fired reduction shinos to C/10 in my oxidation fires and
given them a soak in oxidation during the cooling. They sometimes get
great color from this, but all is dependent on whether they got
reduction during the first firing.
Glad you tried the soak, now experiment with draw trials to determine
the best point at which to saok for maximum microcrystalline growth.
Cheers. Hank in Eugene
murrow.biz/hank
On Jul 15, 2004, at 5:46 AM, Des & Jan Howard wrote:
> Hank
> We have tried the lengthy oxidation soak at ~1050oC
> on the way down from a Cone 11 firing with excellent results
> on red shino, magnesia & celadon glazes.
> Question.
> Have you or anyone on Clayart tried taking pots previously fired
> to say Cone 11 & refiring up to ~1050oC for a lengthy oxidation soak?
David Beumee on thu 15 jul 04
Hank wrote:
> Glad you tried the soak, now experiment with draw trials to determine
> the best point at which to saok for maximum microcrystalline growth.
I fire reduction atmospheres to cone 10, and I've often wondered if there's a way to get some texture in a glaze by producing crystals, i.e. adding zinc to some of my reduction glazes and soaking the firing at a certain temperature. So it was with great interest that I read the following quote from Susan Peterson's second edition of Working with Clay; "Simply stated, add 20% or more zinc oxide to any high temperature glaze; hold the the kiln for several hours at cone 5 on the cooling side of the firing, and tomorrow you may have crystals."
Has anyone tried this in a gas reduction kiln, firing to cone 10? Does the fluxing action of such a quantity of zinc cause alot of running? It sounds to me that it would be prudent to fire some tests in cups, or even better draw rings in cups.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Dear Des;
>
> Yes, I have re-fired reduction shinos to C/10 in my oxidation fires and
> given them a soak in oxidation during the cooling. They sometimes get
> great color from this, but all is dependent on whether they got
> reduction during the first firing.
>
> Glad you tried the soak, now experiment with draw trials to determine
> the best point at which to saok for maximum microcrystalline growth.
>
> Cheers. Hank in Eugene
> murrow.biz/hank
>
> On Jul 15, 2004, at 5:46 AM, Des & Jan Howard wrote:
>
> > Hank
> > We have tried the lengthy oxidation soak at ~1050oC
> > on the way down from a Cone 11 firing with excellent results
> > on red shino, magnesia & celadon glazes.
> > Question.
> > Have you or anyone on Clayart tried taking pots previously fired
> > to say Cone 11 & refiring up to ~1050oC for a lengthy oxidation soak?
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
John Hesselberth on thu 15 jul 04
Hi David,
In a reduction atmosphere zinc oxide easily reduces to zinc metal which
boils at 907 deg C. Depending on where your glaze seals over and when
you start reduction you may not have any zinc left in the glaze.
Regards,
John
On Thursday, July 15, 2004, at 04:51 PM, David Beumee wrote:
> Has anyone tried this in a gas reduction kiln, firing to cone 10?
> Does the fluxing action of such a quantity of zinc cause alot of
> running? It sounds to me that it would be prudent to fire some tests
> in cups, or even better draw rings in cups.
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ivor and Olive Lewis on fri 16 jul 04
Dear David Beumee,
You say the suggestion is to <<...add 20% or more zinc oxide to any
high temperature glaze; hold the kiln for several hours at cone 5 on
the cooling side of the firing, and tomorrow you may have crystals>>
If crystals do form this chemical reaction will deplete the glaze of
silica. It might be predicted that this will change the stability of
the glaze and lead to some degree of degradation in service.
Whether or not this singular instance might be generalised to all
glazes which throw down crystals when slow cooled is a question that
might be answered by the Boffins at Alfred and other centres of
scientific ceramic study, or by submission of samples to a laboratory
for test.
As some might say "All Caveats apply".
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on fri 16 jul 04
Dear Des,
May I offer this suggestion?
Make a sample of the glaze you wish to refire of a shape and size that
Ron Roy could push through his dilatometer. He will be able to
determine the minimum temperature to which your glaze must be fired
for it to become reactive.
This thought is prompted by reading Alan Caiger Smith's work on Lustre
finishes. He tells us that for success the surface must become
reactive but not be heated so far that the ceramic carrier of the
lustre pigments adhere to the surface of the pot. Firing temperatures
given for this work are in the 625=BA- 675=BA C region.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Des & Jan Howard on fri 16 jul 04
Ivor
This is of course assuming that the crystals formed are a silicate.
Our usual microcrystalline glaze has ~40% silica in the recipe &
the durability does not appear obviously harmed.
With this same glaze if the silica addition falls below ~35% it does craze.
I'm doing some testing with iron phosphate crystal effects so we'll see what happens there.
Regards
Des
Ivor and Olive Lewis wrote:
> If crystals do form this chemical reaction will deplete the glaze of
> silica. It might be predicted that this will change the stability of
> the glaze and lead to some degree of degradation in service.
> Whether or not this singular instance might be generalised to all
> glazes which throw down crystals when slow cooled is a question that
> might be answered by the Boffins at Alfred and other centres of
> scientific ceramic study, or by submission of samples to a laboratory
> for test.
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Des & Jan Howard on fri 16 jul 04
Hank
The reason for the query is that I'm building an fibre electric kiln
specifically to biscuit fire pots for the larger gas kiln & as a
programmable controller will be part of the installation which
is intended to have a max firing temp of 1100o C, the
idea of using the system to soak pots previously fired to
Cone 10/11 reduction crossed my mind.
Regards
Des
Hank Murrow wrote:
> Dear Des;
>
> Yes, I have re-fired reduction shinos to C/10 in my oxidation fires and
> given them a soak in oxidation during the cooling. They sometimes get
> great color from this, but all is dependent on whether they got
> reduction during the first firing.
>
> Glad you tried the soak, now experiment with draw trials to determine
> the best point at which to saok for maximum microcrystalline growth.
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Ron Roy on sat 17 jul 04
Hi David,
It is doubtful because zinc is easily reduced and most if not all will be lost.
Cone 5 seems to me too hot for optimum crystal growth.
I'm surprised SP is not aware that zinc would not be affected by
reduction??? Perhaps she means in only oxidation firings.
And yes - zinc would result in a lot more melting - you would need to
replace other fluxes with the zinc in an oxidation firing.
Also zinc has a negative effect on iron colour - now I wonder - if it is
lost in the reduction firing would it still have the effect on the iron?
RR
> I fire reduction atmospheres to cone 10, and I've often wondered if
>there's a way to get some texture in a glaze by producing crystals, i.e.
>adding zinc to some of my reduction glazes and soaking the firing at a
>certain temperature. So it was with great interest that I read the
>following quote from Susan Peterson's second edition of Working with Clay;
>"Simply stated, add 20% or more zinc oxide to any high temperature glaze;
>hold the the kiln for several hours at cone 5 on the cooling side of the
>firing, and tomorrow you may have crystals."
> Has anyone tried this in a gas reduction kiln, firing to cone 10? Does
>the fluxing action of such a quantity of zinc cause alot of running? It
>sounds to me that it would be prudent to fire some tests in cups, or even
>better draw rings in cups.
>
>David Beumee
>Earth Alchemy Pottery
>Lafayette, CO
>
>
>> Dear Des;
>>
>> Yes, I have re-fired reduction shinos to C/10 in my oxidation fires and
>> given them a soak in oxidation during the cooling. They sometimes get
>> great color from this, but all is dependent on whether they got
>> reduction during the first firing.
>>
>> Glad you tried the soak, now experiment with draw trials to determine
>> the best point at which to saok for maximum microcrystalline growth.
>>
>> Cheers. Hank in Eugene
>> murrow.biz/hank
>>
>> On Jul 15, 2004, at 5:46 AM, Des & Jan Howard wrote:
>>
>> > Hank
>> > We have tried the lengthy oxidation soak at ~1050oC
>> > on the way down from a Cone 11 firing with excellent results
>> > on red shino, magnesia & celadon glazes.
>> > Question.
>> > Have you or anyone on Clayart tried taking pots previously fired
>> > to say Cone 11 & refiring up to ~1050oC for a lengthy oxidation soak?
>>
>>
>>__________________________________________________________________________
>>____
>> Send postings to clayart@lsv.ceramics.org
>>
>> You may look at the archives for the list or change your subscription
>> settings from http://www.ceramics.org/clayart/
>>
>> Moderator of the list is Mel Jacobson who may be reached at
>>melpots@pclink.com.
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on sat 17 jul 04
Dear Des,
My remarks were simply in response to the Peterson quotation relating
to the modification of any glaze. To ascertain which of the minerals
will form people might need to consult some of the Equilibrium Phase
Diagrams.
But following your lead, it might be possible to get non silicate
minerals. Zinc Aluminate seems possible if you can fire the right
recipe above 1400=BA and get all of the precursor substances into
solution.
Interesting things to speculate on! !
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
.
David Beumee on sun 18 jul 04
Hi Ron,
You wrote,
> It is doubtful because zinc is easily reduced and most if not all will be lost.
Okay, then is there another material, say rutile, TiO2, talc, cryolite, that is more refractory by nature, that might produce crystalline growth?
> Cone 5 seems to me too hot for optimum crystal growth.
On the way down, what's the optimum temp. to hold the firing and allow crystals to grow?
> Also zinc has a negative effect on iron colour - now I wonder - if it is
> lost in the reduction firing would it still have the effect on the iron?
Sounds like a whole bunch of tests to me. I wonder about Dave Finkelnburg's suggestion of putting another glaze on top of the glaze containing zinc.
I'm surprised noone has explored and written about crystalline growth in reduction firings to cone 10.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Hi David,
>
> It is doubtful because zinc is easily reduced and most if not all will be lost.
>
> Cone 5 seems to me too hot for optimum crystal growth.
>
> I'm surprised SP is not aware that zinc would not be affected by
> reduction??? Perhaps she means in only oxidation firings.
>
> And yes - zinc would result in a lot more melting - you would need to
> replace other fluxes with the zinc in an oxidation firing.
>
> Also zinc has a negative effect on iron colour - now I wonder - if it is
> lost in the reduction firing would it still have the effect on the iron?
>
> RR
>
>
> > I fire reduction atmospheres to cone 10, and I've often wondered if
> >there's a way to get some texture in a glaze by producing crystals, i.e.
> >adding zinc to some of my reduction glazes and soaking the firing at a
> >certain temperature. So it was with great interest that I read the
> >following quote from Susan Peterson's second edition of Working with Clay;
> >"Simply stated, add 20% or more zinc oxide to any high temperature glaze;
> >hold the the kiln for several hours at cone 5 on the cooling side of the
> >firing, and tomorrow you may have crystals."
> > Has anyone tried this in a gas reduction kiln, firing to cone 10? Does
> >the fluxing action of such a quantity of zinc cause alot of running? It
> >sounds to me that it would be prudent to fire some tests in cups, or even
> >better draw rings in cups.
> >
> >David Beumee
> >Earth Alchemy Pottery
> >Lafayette, CO
> >
> >
> >> Dear Des;
> >>
> >> Yes, I have re-fired reduction shinos to C/10 in my oxidation fires and
> >> given them a soak in oxidation during the cooling. They sometimes get
> >> great color from this, but all is dependent on whether they got
> >> reduction during the first firing.
> >>
> >> Glad you tried the soak, now experiment with draw trials to determine
> >> the best point at which to saok for maximum microcrystalline growth.
> >>
> >> Cheers. Hank in Eugene
> >> murrow.biz/hank
> >>
> >> On Jul 15, 2004, at 5:46 AM, Des & Jan Howard wrote:
> >>
> >> > Hank
> >> > We have tried the lengthy oxidation soak at ~1050oC
> >> > on the way down from a Cone 11 firing with excellent results
> >> > on red shino, magnesia & celadon glazes.
> >> > Question.
> >> > Have you or anyone on Clayart tried taking pots previously fired
> >> > to say Cone 11 & refiring up to ~1050oC for a lengthy oxidation soak?
> >>
> >>
> >>__________________________________________________________________________
> >>____
> >> Send postings to clayart@lsv.ceramics.org
> >>
> >> You may look at the archives for the list or change your subscription
> >> settings from http://www.ceramics.org/clayart/
> >>
> >> Moderator of the list is Mel Jacobson who may be reached at
> >>melpots@pclink.com.
> >
> >______________________________________________________________________________
> >Send postings to clayart@lsv.ceramics.org
> >
> >You may look at the archives for the list or change your subscription
> >settings from http://www.ceramics.org/clayart/
> >
> >Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy on sun 18 jul 04
Hi Des,
I've refired several glazes to 04 in a bisque firing and gotten results -
but have not soaked.
Judging from my dilatometer experiments - I see my cone 10 glazes getting
soft around 800C - which indicates that cone 04 may be over kill. This is
supported by the literature I have read on stricking - which says refiring
to a low bisque temperature is enough.
What you don't want to do is start remelting the crystals.
Let us know if you do the experiments!
RR
>We have tried the lengthy oxidation soak at ~1050oC
>on the way down from a Cone 11 firing with excellent results
>on red shino, magnesia & celadon glazes.
>Question.
>Have you or anyone on Clayart tried taking pots previously fired
>to say Cone 11 & refiring up to ~1050oC for a lengthy oxidation soak?
>Des
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Des & Jan Howard on mon 19 jul 04
Ron
Thanks, your reply is just what I was after.
The fibre biscuit kiln I mentioned will have to run off our
single phase supply, so if I can fire lower a bigger kiln can be built.
As soon as it is up & running some experiments will start.
Jan is rapt in the idea of an electric "bicky" kiln,
press the button/s & walk away!
Des
Ron Roy wrote:
> I've refired several glazes to 04 in a bisque firing and gotten results -
> but have not soaked.
>
> Judging from my dilatometer experiments - I see my cone 10 glazes getting
> soft around 800C - which indicates that cone 04 may be over kill. This is
> supported by the literature I have read on stricking - which says refiring
> to a low bisque temperature is enough.
>
> What you don't want to do is start remelting the crystals.
>
> Let us know if you do the experiments!
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Ron Roy on tue 20 jul 04
Hi David,
Any material which survives the melting - remaining in a crystalline state
- will provide seeds for crystals to grow on, Titanium would be one - tin
and zirconium silicate (zircopax, superpax, opax) would be others.
Certainly not talc or cryolite as they would both go into solution in any
high firing.
When zinc is used in high quantities it being used as a flux first and as a
constituant of certain kinds of crystals as they form on cooling - the
process is speeded up when unmelted crystals are provided as seeds.
Crystals need silica to form - and alumina is a crystal inhibitor - which
explains why crystal glazes tend to run so much.
I am not talking about matte glazes by the way - but large crystals
surrounded by shiny glaze - I assume that is what interests you.
The optimum temperature to hold at would be determined by glaze composition
- and - as others have suggested - pulled glaze rings would provide the
evidence.
If you are refiring - that may be the quickest way to determine optimum
temperature range for crystal development. Have some crystals - on draw
rings. Advance temperature until crystals start to remelt (get smaller) -
you then know the upper temperature at which crystals begin to form - so
start slowing or holding 100C below that.
If a glaze is dilatometered - then you know when (at what temperature) it
freezes - so no use trying to grow crystals below that.
Now I am guessing - if the freezing temperature is 700C and the crystals
start melting at 950C then perhaps a hold at 250 divided by two = 125C - so
the best hold would be around 825 to 900C ?
I really don't know but it would have to be between 700C and 950 - that
much is clear - crystals can't grow and melt at the same time and can't
grow when the glazes is not pyroplastic.
RR
>> It is doubtful because zinc is easily reduced and most if not all will
>>be lost.
>
>Okay, then is there another material, say rutile, TiO2, talc, cryolite,
>that is more refractory by nature, that might produce crystalline growth?
>
>> Cone 5 seems to me too hot for optimum crystal growth.
>
>On the way down, what's the optimum temp. to hold the firing and allow
>crystals to grow?
>
>> Also zinc has a negative effect on iron colour - now I wonder - if it is
>> lost in the reduction firing would it still have the effect on the iron?
>
>Sounds like a whole bunch of tests to me. I wonder about Dave
>Finkelnburg's suggestion of putting another glaze on top of the glaze
>containing zinc.
>I'm surprised noone has explored and written about crystalline growth in
>reduction firings to cone 10.
>
>David Beumee
>Earth Alchemy Pottery
>Lafayette, CO
>
>
>> Hi David,
>>
>> It is doubtful because zinc is easily reduced and most if not all will
>>be lost.
>>
>> Cone 5 seems to me too hot for optimum crystal growth.
>>
>> I'm surprised SP is not aware that zinc would not be affected by
>> reduction??? Perhaps she means in only oxidation firings.
>>
>> And yes - zinc would result in a lot more melting - you would need to
>> replace other fluxes with the zinc in an oxidation firing.
>>
>> Also zinc has a negative effect on iron colour - now I wonder - if it is
>> lost in the reduction firing would it still have the effect on the iron?
>>
>> RR
>>
>>
>> > I fire reduction atmospheres to cone 10, and I've often wondered if
>> >there's a way to get some texture in a glaze by producing crystals, i.e.
>> >adding zinc to some of my reduction glazes and soaking the firing at a
>> >certain temperature. So it was with great interest that I read the
>> >following quote from Susan Peterson's second edition of Working with Clay;
>> >"Simply stated, add 20% or more zinc oxide to any high temperature glaze;
>> >hold the the kiln for several hours at cone 5 on the cooling side of the
>> >firing, and tomorrow you may have crystals."
>> > Has anyone tried this in a gas reduction kiln, firing to cone 10? Does
>> >the fluxing action of such a quantity of zinc cause alot of running? It
>> >sounds to me that it would be prudent to fire some tests in cups, or even
>> >better draw rings in cups.
>> >
>> >David Beumee
>> >Earth Alchemy Pottery
>> >Lafayette, CO
>> >
>> >
>> >> Dear Des;
>> >>
>> >> Yes, I have re-fired reduction shinos to C/10 in my oxidation fires and
>> >> given them a soak in oxidation during the cooling. They sometimes get
>> >> great color from this, but all is dependent on whether they got
>> >> reduction during the first firing.
>> >>
>> >> Glad you tried the soak, now experiment with draw trials to determine
>> >> the best point at which to saok for maximum microcrystalline growth.
>> >>
>> >> Cheers. Hank in Eugene
>> >> murrow.biz/hank
>> >>
>> >> On Jul 15, 2004, at 5:46 AM, Des & Jan Howard wrote:
>> >>
>> >> > Hank
>> >> > We have tried the lengthy oxidation soak at ~1050oC
>> >> > on the way down from a Cone 11 firing with excellent results
>> >> > on red shino, magnesia & celadon glazes.
>> >> > Question.
>> >> > Have you or anyone on Clayart tried taking pots previously fired
>> >> > to say Cone 11 & refiring up to ~1050oC for a lengthy oxidation soak?
>> >>
>> >>
>> >>__________________________________________________________________________
>> >>____
>> >> Send postings to clayart@lsv.ceramics.org
>> >>
>> >> You may look at the archives for the list or change your subscription
>> >> settings from http://www.ceramics.org/clayart/
>> >>
>> >> Moderator of the list is Mel Jacobson who may be reached at
>> >>melpots@pclink.com.
>> >
>>
>>>_________________________________________________________________________
>>_____
>> >Send postings to clayart@lsv.ceramics.org
>> >
>> >You may look at the archives for the list or change your subscription
>> >settings from http://www.ceramics.org/clayart/
>> >
>> >Moderator of the list is Mel Jacobson who may be reached at
>>melpots@pclink.com.
>>
>> Ron Roy
>> RR#4
>> 15084 Little Lake Road
>> Brighton, Ontario
>> Canada
>> K0K 1H0
>> Phone: 613-475-9544
>> Fax: 613-475-3513
>>
>>
>>__________________________________________________________________________
>>____
>> Send postings to clayart@lsv.ceramics.org
>>
>> You may look at the archives for the list or change your subscription
>> settings from http://www.ceramics.org/clayart/
>>
>> Moderator of the list is Mel Jacobson who may be reached at
>>melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
