Dave Finkelnburg on tue 23 oct 01
Ron, David, Sylvia and others interested in zinc,
I have wondered for some time if the zinc melts early in the firing
(Rhodes says it melts about cone 02) and acts as a flux before at least some
of it vaporizes out of the glaze near the end of a cone 10 firing? That
would leave it exerting some influence on the finished glaze but still allow
for the fact that it does vaporize at high temperature. Your experiments,
David, seem to confirm this hypothesis. I would expect that zinc would
vaporize less from a molten glaze than as a pure powder.
For what it's worth....
Dave Finkelnburg, glazing in Idaho
From: David Hendley
>I have done extensive testing with zinc oxide in reduction firing.
>A couple of years ago, I selected 6 glazes with high percentages
>of zinc oxide in them (at least 5% zinc).
>I mixed up a batch of each, as written, and a batch omitting the
>zinc oxide.
>I glazed 3 test tiles with each variation.
>The results were clear and undeniable: zinc oxide has an effect
>in some reduction glazes.
>In half the glazes, the 2 variations showed no difference, but
>in the other half, the tests without the zinc oxide came out
>differently than those with the zinc, on all 6 test tiles.
>I reduce my kiln heavily, early, and constantly, so there is no
>question the glazes were reduced. Lots of copper reds and
>rutile blues in these firings.
>When I fired a teaspoonful of straight zinc oxide, the powder
>disappeared, and there was no puddle of melted material,
>but there was white flashing and vapor marks on the test
>plate and other near-by surfaces.
David Hendley on tue 23 oct 01
As much as I value and respect Ron Roy's knowledge of glazes,
I have to agree with Sylvia.
As I've said before, if theory says one thing and experience says
another, I'll go with reality over theory every time.
I have done extensive testing with zinc oxide in reduction firing.
A couple of years ago, I selected 6 glazes with high percentages
of zinc oxide in them (at least 5% zinc).
I mixed up a batch of each, as written, and a batch omitting the
zinc oxide.
I glazed 3 test tiles with each variation.
The results were clear and undeniable: zinc oxide has an effect
in some reduction glazes.
In half the glazes, the 2 variations showed no difference, but
in the other half, the tests without the zinc oxide came out
differently than those with the zinc, on all 6 test tiles.
I even showed Ron the test tiles at the Denver NCECA.
I reduce my kiln heavily, early, and constantly, so there is no
question the glazes were reduced. Lots of copper reds and
rutile blues in these firings.
When I fired a teaspoonful of straight zinc oxide, the powder
disappeared, and there was no puddle of melted material,
but there was white flashing and vapor marks on the test
plate and other near-by surfaces.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "Mark Mondloch"
To:
Sent: Tuesday, October 23, 2001 7:40 AM
Subject: Re: RR vaporized zinc
> > Probably no use in putting in the Zink Oxide if you are firing in
> > reduction. There is reduction at some stages even in oxidation firing -
> > especially if once firing - so even in oxidation firing it is probably
> > vaporized.
>
> Hi Ron,
> I know this is conventional wisdom, but it doesn't seem to jibe with my
> personal experience. I don't reduce heavily- short body reduction(10 min)
at
> cone 08, then neutral until glaze reduction. I use a high zinc rutile blue
> glaze. I have tried removing the zinc from the recipe, but then it loses
the
> blue color. It also loses the blue color if reduced very heavily, but
under
> my normal firing conditions it doesn't. Could the zinc be somehow
protected
> from being volatized from reduction once it has started to be involved in
> the glaze melt?
>
> Awhile back I did a test. On a bisque plate I put a compacted teaspoon
full
> of each of the glaze ingredients that I normally use. I fired this plate
> along with a normal glaze load. The little pile of zinc oxide shrunk in
size
> some but certainly did not disappear. Would you consider this a fair test
to
> see if the zinc is sticking around in my firings?
>
> Actually, I'd recommend anyone doing this test with their own glaze
> materials as it was very interesting to see how the individual materials
act
> all by themselves.
> Sylvia
> ---
> Mark & Sylvia Mondloch
> Silver Creek Pottery & Forge
> W6725 Hwy 144
> Random Lake ,Wi 53075
> HotArt@silvercreekpottery.com
> http://www.silvercreekpottery.com
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Earl Brunner on tue 23 oct 01
We have had this discussion in the past, I can't remember if it was at a
workshop or here, but I think that the point David is making here is
that, even if the zinc is no longer present in the glaze AFTER reduction
firing, it can still influence the behavior of the glaze during the
firing. The fact that in some glazes the presence of zinc seems to make
a difference in the final product while in others it doesn't would seem
to bear this out. It's really immaterial whether there is any zinc left
in the glaze at the end of the firing if DURING the firing the presence
of the zinc causes something to happen.
You can get an artificially induced reduction in copper red glazes by
including finely ground silicon carbide into the glaze in an oxidation
firing. Is all of the silicon carbide still in the glaze at the end?
If so, what is causing the localized reduction in the glaze? (On the
other hand I might not have a clue what I'm talking about on this one.)
David Hendley wrote:
> As much as I value and respect Ron Roy's knowledge of glazes,
> I have to agree with Sylvia.
> As I've said before, if theory says one thing and experience says
> another, I'll go with reality over theory every time.
>
> I have done extensive testing with zinc oxide in reduction firing.
> A couple of years ago, I selected 6 glazes with high percentages
> of zinc oxide in them (at least 5% zinc).
> I mixed up a batch of each, as written, and a batch omitting the
> zinc oxide.
> I glazed 3 test tiles with each variation.
>
> The results were clear and undeniable: zinc oxide has an effect
> in some reduction glazes.
--
Earl Brunner
http://coyote.accessnv.com/bruec/
bruec@anv.net
John Hesselberth on wed 24 oct 01
on 10/23/01 10:05 PM, Earl Brunner at bruec@ANV.NET wrote:
> We have had this discussion in the past, I can't remember if it was at a
> workshop or here, but I think that the point David is making here is
> that, even if the zinc is no longer present in the glaze AFTER reduction
> firing, it can still influence the behavior of the glaze during the
> firing. The fact that in some glazes the presence of zinc seems to make
> a difference in the final product while in others it doesn't would seem
> to bear this out. It's really immaterial whether there is any zinc left
> in the glaze at the end of the firing if DURING the firing the presence
> of the zinc causes something to happen.
Hi Earl, David and others,
To me the point of being careful with zinc in reduction is one of a warning
flag, not a statement of absolutes. Zinc oxide is easily reduced to zinc
metal and zinc metal boils at our firing temperatures. This does not mean
that all the zinc gets reduced and leaves. Once a glaze is in the glassy
state, most of the reduction takes place at or near the surface. If all the
zinc has been reduced while the glaze is still somewhere between powder and
glass, then it probably all leaves and has little effect on the glaze. If
you are in oxidation or very light reduction until glass is formed, some
probably remains in the glaze.
I think it would be fair to say that zinc-containing glazes may be quite
variable and unpredictable in reduction depending on how carefully you
duplicate conditions firing to firing and how uniform the interior of your
kiln is. In addition you are certainly putting some zinc into the
atmosphere which probably quickly reoxidizes to zinc oxide. You should only
do this under very well ventilated conditions.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Mark Mondloch on wed 24 oct 01
My zinc rutile blue glaze is one of the glazes that was giving me sporadic
blistering problems (cone10 propane MFT -light reduction) until I started
venting the kiln during cool-down from top temp to about 1800F. Now I get no
blisters at all. So with this discussion, my thinking now is that perhaps
the zinc (that which is still left in the glaze after reaching temp) was
getting reduced and boiled during the initial cooling stage . By venting I
am maintaining a cleaner atmosphere? The oxyprobe reads as though the
atmosphere is oxidizing even without venting, but the difference in my
glazes has been dramatic. Or is there something else going on that I'm
missing?
Sylvia
---
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
HotArt@silvercreekpottery.com
http://www.silvercreekpottery.com
> Hi Earl, David and others,
>
> To me the point of being careful with zinc in reduction is one of a
warning
> flag, not a statement of absolutes. Zinc oxide is easily reduced to zinc
> metal and zinc metal boils at our firing temperatures. This does not mean
> that all the zinc gets reduced and leaves. Once a glaze is in the glassy
> state, most of the reduction takes place at or near the surface. If all
the
> zinc has been reduced while the glaze is still somewhere between powder
and
> glass, then it probably all leaves and has little effect on the glaze. If
> you are in oxidation or very light reduction until glass is formed, some
> probably remains in the glaze.
>
> I think it would be fair to say that zinc-containing glazes may be quite
> variable and unpredictable in reduction depending on how carefully you
> duplicate conditions firing to firing and how uniform the interior of your
> kiln is. In addition you are certainly putting some zinc into the
> atmosphere which probably quickly reoxidizes to zinc oxide. You should
only
> do this under very well ventilated conditions.
>
> Regards,
>
> John
> Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
>
> "The life so short, the craft so long to learn." Chaucer's translation of
> Hippocrates, 5th cent. B.C.
Paul Lewing on wed 24 oct 01
on 10/24/01 12:59 AM, David Hendley at hendley@TYLER.NET wrote:
> The results were clear and undeniable: zinc oxide has an effect
> in some reduction glazes.
> In half the glazes, the 2 variations showed no difference, but
> in the other half, the tests without the zinc oxide came out
> differently than those with the zinc, on all 6 test tiles.
David, do you have any hypothesis about what made the difference in whether
or not the zinc had an effect?
Paul Lewing, Seattle
Paul Taylor on thu 25 oct 01
Dear all
could what matters be the reducing effect on the coloring oxide.
Particularly iron as it needs to be reduced at a low temperature to act as a
flux and go blue. Is the zinc useful in sealing this reaction by combining
the reduced oxides with silica at an early stage in the firing and
preventing their reoxidization ???.
--
Do not take anything for granted especialy the acuracy of my posts.
Regards Paul Taylor
> From: David Hendley
> Reply-To: Ceramic Arts Discussion List
> Date: Tue, 23 Oct 2001 17:59:33 -0700
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Zinc oxide does influence reduction glazes
>
> As much as I value and respect Ron Roy's knowledge of glazes,
> I have to agree with Sylvia.
> As I've said before, if theory says one thing and experience says
> another, I'll go with reality over theory every time.
>
> I have done extensive testing with zinc oxide in reduction firing.
> A couple of years ago, I selected 6 glazes with high percentages
> of zinc oxide in them (at least 5% zinc).
> I mixed up a batch of each, as written, and a batch omitting the
> zinc oxide.
> I glazed 3 test tiles with each variation.
>
> The results were clear and undeniable: zinc oxide has an effect
> in some reduction glazes.
> In half the glazes, the 2 variations showed no difference, but
> in the other half, the tests without the zinc oxide came out
> differently than those with the zinc, on all 6 test tiles.
> I even showed Ron the test tiles at the Denver NCECA.
>
> I reduce my kiln heavily, early, and constantly, so there is no
> question the glazes were reduced. Lots of copper reds and
> rutile blues in these firings.
>
> When I fired a teaspoonful of straight zinc oxide, the powder
> disappeared, and there was no puddle of melted material,
> but there was white flashing and vapor marks on the test
> plate and other near-by surfaces.
>
> David Hendley
> Maydelle, Texas
> hendley@tyler.net
> http://www.farmpots.com
>
>
>
>
>
>
>
> ----- Original Message -----
> From: "Mark Mondloch"
> To:
> Sent: Tuesday, October 23, 2001 7:40 AM
> Subject: Re: RR vaporized zinc
>
>
>>> Probably no use in putting in the Zink Oxide if you are firing in
>>> reduction. There is reduction at some stages even in oxidation firing -
>>> especially if once firing - so even in oxidation firing it is probably
>>> vaporized.
>>
>> Hi Ron,
>> I know this is conventional wisdom, but it doesn't seem to jibe with my
>> personal experience. I don't reduce heavily- short body reduction(10 min)
> at
>> cone 08, then neutral until glaze reduction. I use a high zinc rutile blue
>> glaze. I have tried removing the zinc from the recipe, but then it loses
> the
>> blue color. It also loses the blue color if reduced very heavily, but
> under
>> my normal firing conditions it doesn't. Could the zinc be somehow
> protected
>> from being volatized from reduction once it has started to be involved in
>> the glaze melt?
>>
>> Awhile back I did a test. On a bisque plate I put a compacted teaspoon
> full
>> of each of the glaze ingredients that I normally use. I fired this plate
>> along with a normal glaze load. The little pile of zinc oxide shrunk in
> size
>> some but certainly did not disappear. Would you consider this a fair test
> to
>> see if the zinc is sticking around in my firings?
>>
>> Actually, I'd recommend anyone doing this test with their own glaze
>> materials as it was very interesting to see how the individual materials
> act
>> all by themselves.
>> Sylvia
>> ---
>> Mark & Sylvia Mondloch
>> Silver Creek Pottery & Forge
>> W6725 Hwy 144
>> Random Lake ,Wi 53075
>> HotArt@silvercreekpottery.com
>> http://www.silvercreekpottery.com
>>
>> 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.
David Hendley on thu 25 oct 01
A couple of people have asked why I think zinc oxide has an effect
on high fire reduction glazes, when we know that all of the zinc
should be volatilized.
I don't know.
I just know the results I see.
I do agree with Ivor, that the evidence of the volatilization of the
zinc can be seen as white flashings in the cooled kiln.
This same flashing appears when welding galvanized steel.
I disagree with Sylvia that a kiln can be reducing while cooling.
Any organics that could possibly be left hanging around at this
point are insignificant, and with no fuel introduced into the kiln
there can be no reduction.
As you know, I am very interested in copper red and titanium blue
glazes. My current theory is that reduction for copper reds
takes place 'from the inside out'.
By that I mean, it is the low temperature 'body reduction' that
is most important. If you miss this early reduction, all the
reduction in the world will not get you a copper red.
Once the glaze sinters it is sealed.
My idea is that it is the oxygen-hungry clay under the glaze that
is drawing oxygen out of the glaze, more than the oxygen
starved environment outside the glaze. I think zinc oxide
could have something to do with this important early reduction.
Just a theory.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "Paul Lewing"
To:
Sent: Wednesday, October 24, 2001 12:32 PM
Subject: Re: Zinc oxide does influence reduction glazes
> on 10/24/01 12:59 AM, David Hendley at hendley@TYLER.NET wrote:
>
> > The results were clear and undeniable: zinc oxide has an effect
> > in some reduction glazes.
> > In half the glazes, the 2 variations showed no difference, but
> > in the other half, the tests without the zinc oxide came out
> > differently than those with the zinc, on all 6 test tiles.
>
> David, do you have any hypothesis about what made the difference in whethe
r
> or not the zinc had an effect?
> Paul Lewing, Seattle
>
Mark Mondloch on fri 26 oct 01
> I disagree with Sylvia that a kiln can be reducing while cooling.
ok... I'm really just searching for an explanation for why venting my kiln
on cool-down seems to have cleaned up my blistering problems. Any other
ideas?
Sylvia-- wondering why in the heck I torture myself worrying about why
something is working instead of just being happy that it is.
---
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
HotArt@silvercreekpottery.com
http://www.silvercreekpottery.com
----- Original Message -----
From: "David Hendley"
To:
Sent: Thursday, October 25, 2001 12:13 PM
Subject: Re: Zinc oxide does influence reduction glazes
> A couple of people have asked why I think zinc oxide has an effect
> on high fire reduction glazes, when we know that all of the zinc
> should be volatilized.
> I don't know.
> I just know the results I see.
>
> I do agree with Ivor, that the evidence of the volatilization of the
> zinc can be seen as white flashings in the cooled kiln.
> This same flashing appears when welding galvanized steel.
> Any organics that could possibly be left hanging around at this
> point are insignificant, and with no fuel introduced into the kiln
> there can be no reduction.
>
> As you know, I am very interested in copper red and titanium blue
> glazes. My current theory is that reduction for copper reds
> takes place 'from the inside out'.
> By that I mean, it is the low temperature 'body reduction' that
> is most important. If you miss this early reduction, all the
> reduction in the world will not get you a copper red.
> Once the glaze sinters it is sealed.
> My idea is that it is the oxygen-hungry clay under the glaze that
> is drawing oxygen out of the glaze, more than the oxygen
> starved environment outside the glaze. I think zinc oxide
> could have something to do with this important early reduction.
> Just a theory.
>
> David Hendley
> Maydelle, Texas
> hendley@tyler.net
> http://www.farmpots.com
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