Earl Krueger on fri 30 apr 04
On Friday, Apr 30, 2004, at 17:02 US/Pacific, Bruce Girrell wrote:
> Why would one bit of iron oxide reduce to one state
> while another next door goes to a different state?
Bruce,
Two kids standing in front of a roller coaster.
Each has only half the money needed for a ticket.
They toss a coin.
The winner gets the loser's money and buys a ticket.
Iron's electron configuration is a bit of a weird duck.
But, when you get it figured out I'll buy your book.
Earl K...
Bothell, WA, USA
Bruce Girrell on fri 30 apr 04
OK, so this year we finally made it to NCECA and while we were walking
around the exhibits we picked up a book by Wang Chun Wen (Beyond the Tien Mu
Shan - Ceramic Art of Chun Wen Wang). Were were totally in awe of his
glazes. Every page was like "Oh wow! Look at _this_ one!" Fireworks and
volcanos exploded on his pots. Rainbows shone. Fairy dust trickled down the
sides.
That was at the beginning of a 2 1/2 week trip out west. I had Clayart set
to nomail while we were gone and when I got back I immediately went to the
archives to see what had been written about NCECA and Wang. Surely there
must have been many others who bought the book and even more who saw it but
didn't buy. Surely there would be a lively discussion of "liquid in liquid
separated" glazes.
Nothing. Zip. Zilch. Nada.
I found a couple of messages from two years ago. I found Chun Wen's website
and an article from a 1997 copy of CM. In the article was his original
recipe, almost as if he were saying, "Here's where I started. You can figure
it out like I did."
OK, but where do you start with something like that? I have a basic bead on
what phase separation in an iron saturated glaze means now, but I have the
feeling that Chun Wen could hand me his exact recipes and I would still have
a long way to go. To me it sounds as though the recipe only puts the proper
ingredients in place and that the real trick with this kind of a glaze is in
the firing.
I can certainly construct line blends to play with different recipes, but
how does one go about setting up a systematic set of firing experiments? How
do I even get close enough in the first place to even begin small variations
one way or another? What causes the phase separation to occur? Why would one
bit of iron oxide reduce to one state while another next door goes to a
different state? When does the phase separation occur in the firing? What
conditions promote it and what conditions inhibit it?
I don't know where to turn to find answers to questions like these. I have
searched for "iron saturated glazes" "phase separation" "liquid - liquid
separation" and similar terms with almost nothing to show for it. I have
found out that phase separation in glass is a very bad thing for nuclear
waste containment. I know approximate silica/alumina ratios and iron oxide
content. I know nothing about how to fire an iron saturated glaze other than
what I have read regarding oil spot glazes and a few vague hints from Wang.
Anybody out there have any clues? Wasn't there anyone else affected by the
work that this man has produced?
Bruce Girrell
"Success is not a word in my vocabulary. I never succeed. I do more research
and make more ceramics until my energy is all gone. I want this energy to
show in my pieces so that when you hold them you can see and feel it." -
Wang Chun Wen
Hank Murrow on sat 1 may 04
Dear Bruce;
You can make a good start by getting two glass formers into your
recipe. I use Phosphorus as my preferred additional glass former,
usually from bone ash, but sometimes from wood ash. The phosphorus
makes a glass that forms within the silicate glass......thus, two phase
glass. fruitwood ash has a lot of Phosphorus, because that is what
fruit needs to develop. The closer to the ends of the branches, the
more Phosphorus content.
Cheers, Hank
www.murrow.biz/hank
On Apr 30, 2004, at 5:02 PM, Bruce Girrell wrote:
> Surely there would be a lively discussion of "liquid in liquid
> separated" glazes.
> Where do you start with something like that?
Don Kopyscinski on sat 1 may 04
Bruce Girrell asks,
<< What causes the phase separation to occur? Why would one
bit of iron oxide reduce to one state while another next door goes to a
different state? When does the phase separation occur in the firing? What
conditions promote it and what conditions inhibit it?>>
Hi Bruce,
To the best of my knowledge the following conditions apply:
(Chemists and Physicists, please chime in and forgive my transgressions)
Two or more different glass formers, RO2, in the same melt
Low levels of alumina to promote mobility in the melted glaze
Full and complete melt of the glaze components. In the proper glaze this
creates a "super saturated solution" which on cooling slowly enough through the
zone of nucleation and precipitation.
A small amount of "seeding agent" in the glaze melt such as, titania sourced
from rutile or illmenite and perhaps a touch of zirconia.
Thick application of glaze - You will often notice a nice fat roll on the
foot of many of the most delicious looking glazes due to a thick application of a
glaze with some fluidity.
You can reach the same cone by a variety of heating profiles, cones indicate
heat work. It is best to fire faster and hotter to melt the cones than slow
and soak. Glaze materials react 10 times faster than body components to heat
work (re:Kingery, Parlemee, or Green...forget which one...could be from "Elements
of Ceramics, Norton") Heating quickly reduces the level of clay body/glaze
interface and thus less alumina is imparted in the bond.
Slow cooling levels in the upper ranges.
Similar to crystalline firings..Fast up, quick cool a few hundred degrees,
soak or slow cool for the next 500 degrees or so. (Read Parmelee, "Ceramic
Glazes", Kingery "Ceramic Masterpieces", Norton, Elements of Ceramics,Yvonne
Hutchinson Cuff, " Ceramic Technology for Potters and Sculptors" and if you can wrap
your mind around it...Kingery's, "Introduction to Ceramics" [too deep for
me...If this is the introduction, I've got a long way to go])
I believe the same phenomena is associated with glazes such as Rutile Blue. I
think the blue comes from the interaction of boron, calcia, titania, and
perhaps a touch of iron. There are minuscule globules of
Sodia-Calcia-Boro-Titanate (to coin a phrase, if this isn't the correct name) glass suspended within
the matrix of the Calcium-Silicate glass. It is my theory that the field
strength of titania causes it to preferentially opacify the calcium borate. The
bluish white almost cloud-like structure present in such a glaze have precipitated
out of the complete melt and produce a different indices of refraction when
light passes through the glaze layer. The light is bent as it hits these little
floating globules of crystalline material suspended in the amorphous, silicate
matrix. It refracts, and reflects, some blue-white wavelengths of the
electromagnetic spectrum as they pass through these suspended globules at differing
speed than the surrounding glaze layer. Our eye perceives this as a bluish hue.
Think of homogenized milk (which goes up fifty cents on Sunday). The fatty
component of the milk is still there. It is broken up into tiny globules that
are suspended in the milk. They agglomerate to a limited extent, but still these
floccules are not large enough to provide them with enough mobility to reach
the surface.
In any super saturated solution, there is a tendency of the solute to
precipitate out to give us a variegated mottled surface in the glaze. The change of
color and hue are due to differing ionic exchanges during phase separation
(getting a little deep for me). Look up "cation exchange", "base exchange", "ionic
bonding strength", "field strength", "adsorption", and "flocculation". There
is much material in the literature that is often glanced over which provide
the answers to such puzzling reactions.
Recently there was a discussion explaining the preferential coloring of
crystals in zinc-silicate glazes low in alumina. Two different coloring oxides in a
traditional "crystalline glaze" will migrate to different portions of the
melt as it cools. This provides such effects as brilliant blue shimmering
crystals suspended in an amber glaze.
Another way is to "throw a little of this, or that, into the glaze", stand
back and see what happens (as Jack Troy once said regarding frits in glaze
decorating media..."whatever bucket happens to be closest to the scale)". The cause
is the same, regardless of our perception of how and why it works.
Having retained bits and pieces from the literature,
Regards,
Don Kopyscinski
Bear Hills Pottery
Newtown, CT
Ivor and Olive Lewis on sat 1 may 04
Dear Bruce,
For starters my suggestion would be to go back to the master
researchers. Try to get hold of the text by David Kingery and Pamela
Vandiver. Nigel Wood, "Chinese Glazes" is another good source of
references. Read what he says about Jun glazes.
Best regards,
Ivor Lewis. Redhill, South Australia
Lee Love on sat 1 may 04
Don Kopyscinski wrote:
>Another way is to "throw a little of this, or that, into the glaze", stand
>back and see what happens (as Jack Troy once said regarding frits in glaze
>decorating media..."whatever bucket happens to be closest to the scale)". The cause
>is the same, regardless of our perception of how and why it works.
>
>
Speaking of alternate approaches:
Just finished glazing the last test tiles for the next wood firing. All
were wet mixed and line blended by the ladle measure and often line
blended. Because I am lucky to have a variety of conditions in my kiln,
I need a minimum of 3 tiles per glaze tested (five would be more ideal
to cover the different places in the kiln. But I don't have the space or
time).
In my teacher's firings, there were a minimum of three
different versions of the same glaze, according to the temperature in
the area of the kiln the ware goes. These three were blended together
for more variety, each having a different amount of kaolin, according to
the temperature in the kiln where they went. To make things even more
complex, the the thickness of the glaze was adjusted to the thickness of
each type of ware, glazing small things first and then adding water for
the larger things. We ended up using the minimum of 3X5, different
versions of the same glaze per kiln load, each having a different amount
of kaolin and/or water. So this traditional technology, while
appearing primitive, pays much more attention to kiln temperature glaze
thickness than what most modern potters do.
One of the advantages of wet mixing and ladle measure is that
you have no materials dust in the air, after you wet mix the individual
materials in bulk outside.
--
in Mashiko, Japan http://mashiko.org
Bruce Girrell on sat 1 may 04
Thanks Ivor, I was hoping you'd chime in on this one.
> For starters my suggestion would be to go back to the master
> researchers. Try to get hold of the text by David Kingery and Pamela
> Vandiver.
Kingery and Vandiver are fairly prolific writers. Are you referring to
_Ceramic Masterpieces - Art, Structure, and Technology_?
> Nigel Wood, "Chinese Glazes" is another good source of
> references. Read what he says about Jun glazes.
Already got another referral to this source. It's on my list.
I appreciate the help
Bruce
Ivor and Olive Lewis on sun 2 may 04
Dear Earl,
You say <>.
Perhaps you would like to explain please.
The picture I get is that Iron follows the electron sequencing without
aberration, unlike Copper, which sits a few places further along the
line and fills its penultimate shell at the expense of the valance
electrons. (Perhaps it is this function which accounts for that
element's looseness, giving it the properties of an alkali metal
element)
As I see it, the big problem with Iron is that it does not combine in
exact numerical amounts with Oxygen. This is a function of the way it
fits into the Oxygen lattice.
Best regards,
Ivor Lewis. Redhill, South Australia
Ivor and Olive Lewis on sun 2 may 04
Dear Bruce,
How I would love to have a copy of the "Ceramic Masterpieces tome". I
might not always agree with their interpretations but I respect their
authority and dedication.
Always a pleasure to put out ideas.
Best regards,
Ivor Lewis. Redhill, South Australia
.
Ron Roy on sun 2 may 04
Hi Bruce,
I'm making some kind of educated guess here but - cooling must be important
because it's when the separation occures.
Certainly Boron tends to separate.
Crystals are a form of separation.
Other than that - I don't know.
RR
>OK, but where do you start with something like that? I have a basic bead on
>what phase separation in an iron saturated glaze means now, but I have the
>feeling that Chun Wen could hand me his exact recipes and I would still have
>a long way to go. To me it sounds as though the recipe only puts the proper
>ingredients in place and that the real trick with this kind of a glaze is in
>the firing.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Bruce Girrell on mon 3 may 04
Sorry for the delayed reply, but it took me a while to digest the amount of
information that you presented. Many thanks.
Don Kopyscinski wrote:
> Two or more different glass formers, RO2, in the same melt
> Low levels of alumina to promote mobility in the melted glaze
> Full and complete melt of the glaze components. In the proper glaze this
> creates a "super saturated solution" which on cooling slowly enough
through the
> zone of nucleation and precipitation.
> A small amount of "seeding agent" in the glaze melt such as, titania
sourced
> from rutile or illmenite and perhaps a touch of zirconia.
In an off-line discussion with another clayarter I was beginning to think
that the phase separated glazes were more similar to oil spots and less
similar to crystalline glazes, but the above certainly sounds like all of
the basics for a crystalline glaze (a number of Wang's pots having "rainbow"
spots, similar to oil spots, are listed as being liquid-liquid phase
separated). This morning I was reading a report on phase separation in
glasses used for immobilization of high level nuclear wastes and the
conclusions were similar to yours. The low alumina was particularly
striking. So these glazes are definitely _not_ similar to oil spots, which
rely on high alumina.
> Thick application of glaze - You will often notice a nice fat roll on the
> foot of many of the most delicious looking glazes due to a thick
application of a
> glaze with some fluidity.
After reading this I went back to Wang's book and looked at the photos,
examining the feet of the pots in particular. Some of them do show an
accumulation of glaze at the base, but many do not. However, most of his
pots have a sharp undercut near the base, which would help minimize any
drooling of the glaze. Sly dog. Hadn't noticed that until now.
> It is best to fire faster and hotter to melt the cones than slow
> and soak.
This one surprised me. I would have thought slow all the way would be the
way to go, but I see the reasoning.
Technical references noted - thanks.
> In any super saturated solution, there is a tendency of the solute to
> precipitate out to give us a variegated mottled surface in the glaze. The
change of
> color and hue are due to differing ionic exchanges during phase separation
I think I get the idea. Wang's red with gold halo on a black background then
implies at least three different phases.
> Another way is to "throw a little of this, or that, into the glaze", stand
> back and see what happens
Ah, yes. A recipe for discovering new and exciting glazes, but I'm not sure
that this method would provide the most direct path to a desired result.
I thank you for your thoughtful and detailed reply. You have given me a lot
to work on.
Bruce Girrell
in sunny, but cool, northern Michigan,
thankful for all the responses on this subject - definitely more than I had
even hoped for on such an esoteric topic.
Ivor and Olive Lewis on mon 3 may 04
Dear Ron,
You may well be right that the separation is influenced by cooling.
But it is more about mutual immiscibility, the fact that neither glass
wets the other. Another factor will be the partitioning response of
the other ingredients. Some will divide proportionally while others
will be selective and go to one or the other.
This can only be resolved by detailed analysis of the glazes
concerned.
Best regards
Ivor Lewis. Redhill, South Australia
.
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