Bert Gibson on sat 16 dec 06
How much does the clay body influence whether a glaze finish is matt of =
glossy? Here is my example:
http://home.comcast.net/~mc6gtest/wsb/html/view.cgi-photo.html--SiteID-30=
97289.html
Glaze was Green Blue Black, Cone 10 Reduction. Fired at the community =
college. Both pieces glazed and fired at the same time. Only difference =
is the left one is a smooth white clay called Dillo and the right one is =
white stoneware. As you can see they both ran. The Dillo one shows a =
little crazing. I expected a difference in results, but not this much. =
Also suprised by the reddish coloring I got. Makes me wonder if someone =
made a mistake in mixing.
Bert Gibson
Daniel Semler on sat 16 dec 06
Hi Bert,
Certainly not uncommon for a more highly fluxed body to do this to an
otherwise matte-ish glaze. I see that with comparison of glazes on
stonewares and porcelains for example. You can even see it between different
porcelains. This is certainly a dramatic example though.
As to your question of mixing errors, were both glazed from the same batch
? Your comment implies not, in which case, of course, mix errors are also
possible.
Thanx
D
Bert Gibson on sat 16 dec 06
Thanks Daniel. It was the same glaze batch. One pot was dipped right
after the other. The thought about the mixing error is just because in
about three years of the continuing ed class, this is the first time we
are seeing the red appear with this glaze.
Bert Gibson
----- Original Message -----
From: "Daniel Semler"
To:
Sent: Saturday, December 16, 2006 7:09 AM
Subject: Re: Green Blue Black
> Hi Bert,
>
> Certainly not uncommon for a more highly fluxed body to do this to
an
> otherwise matte-ish glaze. I see that with comparison of glazes on
> stonewares and porcelains for example. You can even see it between
different
> porcelains. This is certainly a dramatic example though.
>
> As to your question of mixing errors, were both glazed from the same
batch
> ? Your comment implies not, in which case, of course, mix errors are
also
> possible.
>
> Thanx
> D
Dave Finkelnburg on sat 16 dec 06
Hi Bert!
Very interesting question, and a great example!
Body has an effect, but it's limited.
My opinion, worth every bit as much as you are
paying for it, is there are so many variables at work
here you can't identify for certain whether glaze/body
interaction is the cause of the differences in
appearance of these samples. :-(
Causes of glossy glaze are: 1. High content of
glass formers relative to fluxes and alumina, 2.
Rapid cooling, 3. Possibly oxidizing firing atmosphere
so iron doesn't act as a flux. The opposite, a matte
surface, can be caused by the reverse of all 3 or by
high alumina content (contributed by the body) in
glaze due to thin glaze application.
From the glossy sample it is clear the glaze by
itself is glossy. In the matte sample it is either
applied more thinly, OR cooled more slowly, or both.
If your white stoneware were less absorbent or for
another reason got a thinner glaze coat, that would
tend to produce a more matte surface.
In my experience, IF you could put a marker of some
sort in the clay or glaze, and then look for that
marker with a scanning electron microscope, when
viewing a cross section sample, you might be able to
determine, from a statistical sample, the actual fired
glaze thickness, from which you might accurately infer
the applied glaze thickness. Without some information
on the applied glaze thickness this sort of thing is
difficult to sort out, beyond conjecture. About all
you can do is manipulate the variables and try to
reproduce this result.
Unless these pieces were fired side by side, it
would be difficult to say firing conditions were for
certain exactly identical.
Crazing, by the way, is much easier to see in a
glossy glaze than a matte glaze, although matte glazes
seem to craze less.
Regards,
Dave Finkelnburg
--- Bert Gibson wrote:
> How much does the clay body influence whether a
> glaze finish is matt of glossy? Here is my example:
>
>
http://home.comcast.net/~mc6gtest/wsb/html/view.cgi-photo.html--SiteID-3097289.html
>
> Glaze was Green Blue Black, Cone 10 Reduction. Fired
> at the community college. Both pieces glazed and
> fired at the same time. Only difference is the left
> one is a smooth white clay called Dillo and the
> right one is white stoneware. As you can see they
> both ran. The Dillo one shows a little crazing. I
> expected a difference in results, but not this much.
> Also suprised by the reddish coloring I got. Makes
> me wonder if someone made a mistake in mixing.
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Daniel Semler on sat 16 dec 06
Hi Bert,
On the colour though. Both showed green and red so if there was an error
they both got it. It could also have been copper flying around the kiln. I
see copper red flushes on pots like that from time to time. You said it was
a cone 10 redux firing - were there any copper red pieces in that kiln ? I
presume both pieces are believed to have hit about the same temp. Is that so ?
Thanx
D
Ellen Currans on sat 16 dec 06
Hi Bert.
I'm guessing this is a copper green glaze because it has some
similarities to one I use. I have found that mine fires differently
(on the same clay) depending on how thick, how hot, and how reduced.
Applied thickly and more heavily reduced it is greenish black. Cone 9
at the back top of the kiln is darker and more mat. Cone 10 to 11 in
the bottom front of the kiln where the flame really licks produces a
glossy, light green. I usually fire with a light reduction, but if I
get it wrong or at the wrong time, I get more of the darker greens,
with copper red over all. (It does not ever run off the pot though and
is very predictable that way. I do not use kiln wash on my shelves.
Never have.) Sometimes half a platter has a swath of red over the
green, which I figure has something to do with my stacking (very tight)
and trapping reduction for a longer time at the wrong time, followed by
oxidation at Cone 9. I don't do sets of dishes so I have learned to
love the variety I get with a copper glaze. Some people love the
greenish red and others want the pure clear green. I just never take
orders to make them more of the same!
Were your pots fired in different places in the kiln? Of course,
different clays would affect how much glaze was slurped up, but you
could test that by firing more sets of the same clay glazed the same
and fired next to each other.
I checked out the other photos on your website, mugs and bowls and felt
that you have really grown in your throwing and glazing since a few
years back when you were asking about mugs. You have obviously been
hard at work ---working on your bones.
Happy potting!
Ellen Currans
Dundee, Oregon
-----Original Message-----
From: idahopottery@YAHOO.COM
To: CLAYART@LSV.CERAMICS.ORG
Sent: Sat, 16 Dec 2006 2:26 PM
Subject: Re: Green Blue Black
Hi Bert!
Very interesting question, and a great example!
Body has an effect, but it's limited.
My opinion, worth every bit as much as you are
paying for it, is there are so many variables at work
here you can't identify for certain whether glaze/body
interaction is the cause of the differences in
appearance of these samples. :-(
Causes of glossy glaze are: 1. High content of
glass formers relative to fluxes and alumina, 2.
Rapid cooling, 3. Possibly oxidizing firing atmosphere
so iron doesn't act as a flux. The opposite, a matte
surface, can be caused by the reverse of all 3 or by
high alumina content (contributed by the body) in
glaze due to thin glaze application.
From the glossy sample it is clear the glaze by
itself is glossy. In the matte sample it is either
applied more thinly, OR cooled more slowly, or both.
If your white stoneware were less absorbent or for
another reason got a thinner glaze coat, that would
tend to produce a more matte surface.
In my experience, IF you could put a marker of some
sort in the clay or glaze, and then look for that
marker with a scanning electron microscope, when
viewing a cross section sample, you might be able to
determine, from a statistical sample, the actual fired
glaze thickness, from which you might accurately infer
the applied glaze thickness. Without some information
on the applied glaze thickness this sort of thing is
difficult to sort out, beyond conjecture. About all
you can do is manipulate the variables and try to
reproduce this result.
Unless these pieces were fired side by side, it
would be difficult to say firing conditions were for
certain exactly identical.
Crazing, by the way, is much easier to see in a
glossy glaze than a matte glaze, although matte glazes
seem to craze less.
Regards,
Dave Finkelnburg
--- Bert Gibson wrote:
> How much does the clay body influence whether a
> glaze finish is matt of glossy? Here is my example:
>
>
http://home.comcast.net/~mc6gtest/wsb/html/view.cgi-photo.html--SiteID-30
97289.html
>
> Glaze was Green Blue Black, Cone 10 Reduction. Fired
> at the community college. Both pieces glazed and
> fired at the same time. Only difference is the left
> one is a smooth white clay called Dillo and the
> right one is white stoneware. As you can see they
> both ran. The Dillo one shows a little crazing. I
> expected a difference in results, but not this much.
> Also suprised by the reddish coloring I got. Makes
> me wonder if someone made a mistake in mixing.
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Bert Gibson on sun 17 dec 06
I am assuming that the pieces were together in the kiln since I left
them next to each other on the shelves waiting to be loaded.
As far as I know the school offers no copper red glaze for us to use.
Other students work on stoneware have gotten more of a pale pink/mauve
color than the dark red color I got here. In the three years I've gone
to this school this glaze has always just produced a pale green black
color.
I am eager now for the next semester to start so I can see if these
results happen again. Funny this happens just as I was getting bored
with the school glazes.
Bert Gibson
----- Original Message -----
From: "Daniel Semler"
To:
Sent: Saturday, December 16, 2006 4:42 PM
Subject: Re: Green Blue Black
> Hi Bert,
>
> On the colour though. Both showed green and red so if there was an
error
> they both got it. It could also have been copper flying around the
kiln. I
> see copper red flushes on pots like that from time to time. You said
it was
> a cone 10 redux firing - were there any copper red pieces in that kiln
? I
> presume both pieces are believed to have hit about the same temp. Is
that so ?
>
> Thanx
> D
Bert Gibson on mon 18 dec 06
Thanks Ellen and Dave for your thoughts and experiences. I'm eager for
the next semester to start so I can try this glaze again.
The pots were glazed one after the other and set on the shelf next to
each other to be loaded in the kiln. I would guess they were placed next
to each other, but I don't know. The Dillo is a smooth tight clay body.
I would assume that the glaze went on thinner on that pot, but that pot
had more runs touch the shelf. The glaze is a matte glaze and the glossy
result is what prompted me to post it to Clayart. I'd post the recipe,
but I haven't found it yet.
Ellen, thanks for the encouraging words about my progress. Just what I
needed to read after a "trying" day in the studio.
Bert Gibson
----- Original Message -----
From: "Ellen Currans"
To:
Sent: Saturday, December 16, 2006 5:05 PM
Subject: Re: Green Blue Black
> Hi Bert.
>
> I'm guessing this is a copper green glaze because it has some
> similarities to one I use. I have found that mine fires differently
> (on the same clay) depending on how thick, how hot, and how reduced.
> Applied thickly and more heavily reduced it is greenish black. Cone 9
> at the back top of the kiln is darker and more mat. Cone 10 to 11 in
> the bottom front of the kiln where the flame really licks produces a
> glossy, light green. I usually fire with a light reduction, but if I
> get it wrong or at the wrong time, I get more of the darker greens,
> with copper red over all. (It does not ever run off the pot though and
> is very predictable that way. I do not use kiln wash on my shelves.
> Never have.) Sometimes half a platter has a swath of red over the
> green, which I figure has something to do with my stacking (very
tight)
> and trapping reduction for a longer time at the wrong time, followed
by
> oxidation at Cone 9. I don't do sets of dishes so I have learned to
> love the variety I get with a copper glaze. Some people love the
> greenish red and others want the pure clear green. I just never take
> orders to make them more of the same!
>
> Were your pots fired in different places in the kiln? Of course,
> different clays would affect how much glaze was slurped up, but you
> could test that by firing more sets of the same clay glazed the same
> and fired next to each other.
>
> I checked out the other photos on your website, mugs and bowls and
felt
> that you have really grown in your throwing and glazing since a few
> years back when you were asking about mugs. You have obviously been
> hard at work ---working on your bones.
>
> Happy potting!
>
> Ellen Currans
> Dundee, Oregon
>
> -----Original Message-----
> From: idahopottery@YAHOO.COM
> To: CLAYART@LSV.CERAMICS.ORG
> Sent: Sat, 16 Dec 2006 2:26 PM
> Subject: Re: Green Blue Black
>
> Hi Bert!
> Very interesting question, and a great example!
> Body has an effect, but it's limited.
> My opinion, worth every bit as much as you are
> paying for it, is there are so many variables at work
> here you can't identify for certain whether glaze/body
> interaction is the cause of the differences in
> appearance of these samples. :-(
> Causes of glossy glaze are: 1. High content of
> glass formers relative to fluxes and alumina, 2.
> Rapid cooling, 3. Possibly oxidizing firing atmosphere
> so iron doesn't act as a flux. The opposite, a matte
> surface, can be caused by the reverse of all 3 or by
> high alumina content (contributed by the body) in
> glaze due to thin glaze application.
> From the glossy sample it is clear the glaze by
> itself is glossy. In the matte sample it is either
> applied more thinly, OR cooled more slowly, or both.
> If your white stoneware were less absorbent or for
> another reason got a thinner glaze coat, that would
> tend to produce a more matte surface.
> In my experience, IF you could put a marker of some
> sort in the clay or glaze, and then look for that
> marker with a scanning electron microscope, when
> viewing a cross section sample, you might be able to
> determine, from a statistical sample, the actual fired
> glaze thickness, from which you might accurately infer
> the applied glaze thickness. Without some information
> on the applied glaze thickness this sort of thing is
> difficult to sort out, beyond conjecture. About all
> you can do is manipulate the variables and try to
> reproduce this result.
> Unless these pieces were fired side by side, it
> would be difficult to say firing conditions were for
> certain exactly identical.
> Crazing, by the way, is much easier to see in a
> glossy glaze than a matte glaze, although matte glazes
> seem to craze less.
> Regards,
> Dave Finkelnburg
>
> --- Bert Gibson wrote:
> > How much does the clay body influence whether a
> > glaze finish is matt of glossy? Here is my example:
> >
> >
>
http://home.comcast.net/~mc6gtest/wsb/html/view.cgi-photo.html--SiteID-30
> 97289.html
> >
> > Glaze was Green Blue Black, Cone 10 Reduction. Fired
> > at the community college. Both pieces glazed and
> > fired at the same time. Only difference is the left
> > one is a smooth white clay called Dillo and the
> > right one is white stoneware. As you can see they
> > both ran. The Dillo one shows a little crazing. I
> > expected a difference in results, but not this much.
> > Also suprised by the reddish coloring I got. Makes
> > me wonder if someone made a mistake in mixing.
>
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.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.
>
>
>
________________________________________________________________________
> Check out the new AOL. Most comprehensive set of free safety and
> security tools, free access to millions of high-quality videos from
> across the web, free AOL Mail and more.
>
>
________________________________________________________________________
______
> 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.
>
Bert Gibson on tue 19 dec 06
I found the Green Blue Black recipe.
Cornwall Stone 46
Whiting 34
China Clay 20
Copper Carb 4
Tin Oxide 4
Bert Gibson
----- Original Message -----
From: "Ellen Currans"
To:
Sent: Saturday, December 16, 2006 5:05 PM
Subject: Re: Green Blue Black
> Hi Bert.
>
> I'm guessing this is a copper green glaze because it has some
> similarities to one I use. I have found that mine fires differently
> (on the same clay) depending on how thick, how hot, and how reduced.
> Applied thickly and more heavily reduced it is greenish black. Cone 9
> at the back top of the kiln is darker and more mat. Cone 10 to 11 in
> the bottom front of the kiln where the flame really licks produces a
> glossy, light green. I usually fire with a light reduction, but if I
> get it wrong or at the wrong time, I get more of the darker greens,
> with copper red over all. (It does not ever run off the pot though and
> is very predictable that way. I do not use kiln wash on my shelves.
> Never have.) Sometimes half a platter has a swath of red over the
> green, which I figure has something to do with my stacking (very
tight)
> and trapping reduction for a longer time at the wrong time, followed
by
> oxidation at Cone 9. I don't do sets of dishes so I have learned to
> love the variety I get with a copper glaze. Some people love the
> greenish red and others want the pure clear green. I just never take
> orders to make them more of the same!
>
> Were your pots fired in different places in the kiln? Of course,
> different clays would affect how much glaze was slurped up, but you
> could test that by firing more sets of the same clay glazed the same
> and fired next to each other.
>
> I checked out the other photos on your website, mugs and bowls and
felt
> that you have really grown in your throwing and glazing since a few
> years back when you were asking about mugs. You have obviously been
> hard at work ---working on your bones.
>
> Happy potting!
>
> Ellen Currans
> Dundee, Oregon
>
Ron Roy on wed 20 dec 06
Hi Bert,
This glaze is way short of silica so it will leach copper into acidic food
- best not to use it as a liner.
RR
>I found the Green Blue Black recipe.
>
>Cornwall Stone 46
>Whiting 34
>China Clay 20
>
>Copper Carb 4
>Tin Oxide 4
>
>
>
>Bert Gibson
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Donna Kat on thu 21 dec 06
Your glaze has copper in it and copper will be red or green based on whether
it is reduced or not. I found it impossible (or near impossible to get
perfect reduction so copper glazes when lucky would be gorgeous red, when
unlucky gag me liver red/green.
Donna
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