Avril Farley on sat 19 jan 02
I have been successfully producing a range of crystalline glazed work =
with colours produced from varying mixes of oxides and carbonates. Can =
anyone tell me please why it is that with a cobalt/manganese combination =
invariably the cobalt migrates to the crystal leaving the manganese to =
provide a gold background, and a copper/manganese combination works the =
other way about - i.e green background, gold crystal.
Thanks
Avril in the Forest UK
H.M. Buchanan on sat 19 jan 02
Avril, I think the color combinations depend on the glaze. One of mine does
just the opposite with copper/ manganese(cool chocolate glaze with turquoise
crystals). I just wish there was better information on crystalline glazes.
Every time I read and accept an authority's pronouncements on the why and
hows, I find another with different view or my testing proves something
else. Example pronouncement: To form crystals the formula must have very
little clay. So why am I getting such nice crystals in a formula with 20%
clay?
I figure I may also be able to use the appellation "successfully" with
another 10 years of testing. :>)
Judi Buchanan, In the woods of Mississippi
----- Original Message -----
I have been successfully producing a range of crystalline glazed work with
colours produced from varying mixes of oxides and carbonates. Can anyone
tell me please why it is that with a cobalt/manganese combination invariably
the cobalt migrates to the crystal leaving the manganese to provide a gold
background, and a copper/manganese combination works the other way about -
i.e green background, gold crystal.
Thanks
Avril in the Forest UK
Jocelyn McAuley on sat 19 jan 02
Ah yes, I couldn't quite put my finger on it last night, but I also get
these same results as Judi:
a highly speckled chocolate bronze surface with bluish crystals with my
Mn and Cu combinations.
As to the search for more information, I just found an interesting read
from Ceramic Bulletin that I would recommend you to spy on:
http://www.ceramicbulletin.org/months/2001-09/Karasufeature.pdf
The title of the paper is Effect of Cobalt Oxide and Copper Oxide
Additions to Zinc-containing Soft Porcelain Glazes (by B. Karasu, and
S. Turan)
I was happy to find this research, but I can't help but be frustrated by
the fact that these researchers are publishing experiments that have been
performed 10 years ago by the likes of Derek Clarkson (Ceramic Review no
137, p27-31, 1992) and Dan Turnidge (Turnidge Porcelain, Copyright
April 26, 1990) and without acknowledgment. The findings are the same,
just worded differently in science-speak. I would have been more
enthusiastic if these experiements were performed for the sake of
reproducability and then used as a jumping off point for further
investigations.
Judi, you may find the Karasu and Turan article interesting in that they
investigate the effects of including "triage waste" a mining byproduct
which among several things contains almost 20% Al2O3. They report that
this addition creates those fluffy frilly outer borders/halos (I have a
nice Clarkson inspired iron glaze that does this). This outer halo has
been investigated and described in Clarkson's article I sited (go read
it! Or I can send you a copy). It turns out that these halos contain
gahnite (ZnAl2O4)
Happy learning!
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, Oregon
http://www.ceramicism.com
Hank Murrow on sat 19 jan 02
Jocelyn wrote;
>As to the search for more information, I just found an interesting read
>from Ceramic Bulletin that I would recommend you to spy on:
>http://www.ceramicbulletin.org/months/2001-09/Karasufeature.pdf
>The title of the paper is Effect of Cobalt Oxide and Copper Oxide
>Additions to Zinc-containing Soft Porcelain Glazes (by B. Karasu, and
>S. Turan)
>
>I was happy to find this research, but I can't help but be frustrated by
>the fact that these researchers are publishing experiments that have been
>performed 10 years ago by the likes of Derek Clarkson (Ceramic Review no
>137, p27-31, 1992) and Dan Turnidge (Turnidge Porcelain, Copyright
>April 26, 1990) and without acknowledgment. The findings are the same,
>just worded differently in science-speak. I would have been more
>enthusiastic if these experiements were performed for the sake of
>reproducability and then used as a jumping off point for further
>investigations.
Hey Jocelyn;
Did you know that Dan Turnidge went to U of Oregon, where you are
working?
Cheers, Hank
Ilene Mahler on sat 19 jan 02
I have gotten deep turq backround but not on crystals Do you want to swich
recipes...Ilene in Conn
----- Original Message -----
From: H.M. Buchanan
To:
Sent: Saturday, January 19, 2002 12:36 PM
Subject: Re: oxide performance in macro crystalline glaze
> Avril, I think the color combinations depend on the glaze. One of mine
does
> just the opposite with copper/ manganese(cool chocolate glaze with
turquoise
> crystals). I just wish there was better information on crystalline
glazes.
> Every time I read and accept an authority's pronouncements on the why and
> hows, I find another with different view or my testing proves something
> else. Example pronouncement: To form crystals the formula must have very
> little clay. So why am I getting such nice crystals in a formula with 20%
> clay?
> I figure I may also be able to use the appellation "successfully" with
> another 10 years of testing. :>)
>
> Judi Buchanan, In the woods of Mississippi
>
> ----- Original Message -----
>
> I have been successfully producing a range of crystalline glazed work with
> colours produced from varying mixes of oxides and carbonates. Can anyone
> tell me please why it is that with a cobalt/manganese combination
invariably
> the cobalt migrates to the crystal leaving the manganese to provide a gold
> background, and a copper/manganese combination works the other way about -
> i.e green background, gold crystal.
>
> Thanks
>
> Avril in the Forest UK
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
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>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
mariko cruse on sun 20 jan 02
Dear Mr. Michael Banks,
Thank you very much for posting your erudite chemical explanations on
various aspects of glazes we used.
I would like to begin educating myself on coloring oxides and other
glaze-related chemistry. Could you name some currently available text books
to start out with? I have some organic chemistry background - such as
DNA/RNA and antibody detection/production, but practically no experince with
inorganic oxides commonly used in this wonderful world of pottery. Thanking
you in advance,
Mariko Cruse
----- Original Message -----
From: "Michael Banks"
To:
Sent: Saturday, January 19, 2002 6:34 AM
Subject: Re: oxide performance in macro crystalline glaze
> Avril,
>
> There is an accepted model in chemistry which gives a successful
explanation
> for the observed relative differences (of the colourant oxides you
mention)
> in entering crystals precipitating from a molten silicate liquid
> (crystal/liquid partitioning).
>
> The model is known as crystal field theory and it applies to the
transition
> metals of the periodic table of elements, including Cu, Zn, Co, Ni, Mn
etc.
> It was developed to explain why these metals (when divalent cations) of
> similar radius and electronegativity, showed dissimilar crystal/liquid
> partition coefficients.
>
> Basically these oxides are ranked according to their "crystal field energy
> strength" which is the relative tendency of each of them to enter
octahedral
> sites in precipitating crystals. The crystals forming from slow-cooling,
> low-alumina, zinc crystal glazes are (generally) willemite -zinc
> orthosilicate (Zn2SiO4). Other divalent metal cations can substitute for
> zinc in willemite. In nature, iron and manganese rich willemites are
known
> (troostite).
>
> Cobalt and nickel are high field strength elements relative to manganese
> (intermediate) and copper (low). In fact, copper seems to show no
> particular tendency to strongly partition into willemite crystals even
when
> it is the only colourant oxide present, zinc being a higher field strength
> element.
>
> Does this help?
>
> Michael Banks,
> Nelson,
> New Zealand
>
> ----- Original Message -----
> Avril Farley wrote:
>
> I have been successfully producing a range of crystalline glazed work with
> colours produced from varying mixes of oxides and carbonates. Can anyone
> tell me please why it is that with a cobalt/manganese combination
invariably
> the cobalt migrates to the crystal leaving the manganese to provide a gold
> background, and a copper/manganese combination works the other way about -
> i.e green background, gold crystal.
>
>
____________________________________________________________________________
__
> 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.
Michael Banks on sun 20 jan 02
Avril,
There is an accepted model in chemistry which gives a successful explanation
for the observed relative differences (of the colourant oxides you mention)
in entering crystals precipitating from a molten silicate liquid
(crystal/liquid partitioning).
The model is known as crystal field theory and it applies to the transition
metals of the periodic table of elements, including Cu, Zn, Co, Ni, Mn etc.
It was developed to explain why these metals (when divalent cations) of
similar radius and electronegativity, showed dissimilar crystal/liquid
partition coefficients.
Basically these oxides are ranked according to their "crystal field energy
strength" which is the relative tendency of each of them to enter octahedral
sites in precipitating crystals. The crystals forming from slow-cooling,
low-alumina, zinc crystal glazes are (generally) willemite -zinc
orthosilicate (Zn2SiO4). Other divalent metal cations can substitute for
zinc in willemite. In nature, iron and manganese rich willemites are known
(troostite).
Cobalt and nickel are high field strength elements relative to manganese
(intermediate) and copper (low). In fact, copper seems to show no
particular tendency to strongly partition into willemite crystals even when
it is the only colourant oxide present, zinc being a higher field strength
element.
Does this help?
Michael Banks,
Nelson,
New Zealand
----- Original Message -----
Avril Farley wrote:
I have been successfully producing a range of crystalline glazed work with
colours produced from varying mixes of oxides and carbonates. Can anyone
tell me please why it is that with a cobalt/manganese combination invariably
the cobalt migrates to the crystal leaving the manganese to provide a gold
background, and a copper/manganese combination works the other way about -
i.e green background, gold crystal.
Hank Murrow on sun 20 jan 02
>Dear Mr. Michael Banks,
>
>Thank you very much for posting your erudite chemical explanations on
>various aspects of glazes we used.
>
>I would like to begin educating myself on coloring oxides and other
>glaze-related chemistry. Could you name some currently available text books
>to start out with? I have some organic chemistry background - such as
>DNA/RNA and antibody detection/production, but practically no experince with
>inorganic oxides commonly used in this wonderful world of pottery. Thanking
>you in advance,
>Mariko Cruse
Dear Mariko & Michael;
David Stannard wrote up the following references around this
question a couple of years ago, and I am forwarding them now:
">Get Bob to dig out that Ionic Potential *sculptural bar* I gave
him, and
>close-up photo it with some good lighting. I think the unit
>distances(inches) measures from the brass O ion will correspond to your
>I.P. differences(P, N, S, show up on the end, for reminder) The Si+4, Al+3,
>Na+, etc., though, are at spread-out, weakening distances. The I.P. is *an
>average intensity of attraction/ unit surface area of the ion*-- the charge
>spread out over a larger ion is weaker/unit area, a larger charge
>concentrated over a smaller ionic surface builds a much stronger
>*intensity* of attraction(/unit area) for the O=, or other anions. Maybe
>you can send a photo as attachment.
Linus Pauling figured out these simple
>arithmetic ratios, & I bet his book "The Nature of the Chemical Bond" is
>still the most direct & simple treatment of Ionic Potential around.
>
>I got a *tremendous* lot of imagery out of the opening chapters of
Brian
>Mason's book "Principles of Geochemistry", 1st ed.(Wiley & Sons, N.Y.,
>1952) I didn't like his revised edition-- better for geol. students, maybe,
>but not for me.
>
>W.A.Weyl wrote a book, collected 1930s series of articles from
Ceram. Soc.,
>called "Colored Glasses" (Dawsons of Pall Mall, 1959) which I found *very*
>useful for the static "network former/modifier theory" treatment. Good for
>imagining competing color tendencies. Later he switched to Dynamic
>modelling-- more satisfying for professionals, & for me in principle, but
>too hard to follow & make simple-minded shop use of it!)
>
Hoping some of this might be helpful, Hank
Michael Banks on sun 20 jan 02
As a addendum to my previous post on crystal field theory, here is a partial
list of high field strength elements from:
http://www.unine.ch/chim/chw/Chapter%204.html.
Mn2+ < Ni2+ < Co2+ < Fe2+ < V2+ < Fe3+ < Co3+ < Mn3+ < Mo3+ < Rh3+ < Ru3+ <
Pd4+ < Ir3+ < Pt4+
Note that maganese can preceed cobalt into crystals (violet crystals in blue
glaze) if the more oxidised ion (Mn3+) rather than the divalent ion, is
present. High temperature favours the divalent ion, lower temperatures, the
trivalent ion.
Materials acting as oxidising agents in the glaze, or firing to lower
temperatures than usual (cone 6 rather than cone 9) can facilitate the
preservation of the Mn3+, as can the glass octahedral site promoters -the
sequioxides boric oxide (B2O3) and alumina (Al2O3). Boric oxide has the
added advantage of lowering the firing temperature and glaze viscosity.
Copper has a low field strength, meaning that the metal is roughly equally
partitioned between glass and the crystals (i.e: pale green crystals in
green glass). But, if other colourants are already partitioned into the
crystals, the copper alters their spectral response in interesting ways,
e.g: metallic greys, bronze, gold etc.
Michael
in NZ
----- Original Message -----
From: Avril Farley
To:
Sent: Saturday, January 19, 2002 02:48
Subject: oxide performance in macro crystalline glaze
I have been successfully producing a range of crystalline glazed work with
colours produced from varying mixes of oxides and carbonates. Can anyone
tell me please why it is that with a cobalt/manganese combination invariably
the cobalt migrates to the crystal leaving the manganese to provide a gold
background, and a copper/manganese combination works the other way about -
i.e green background, gold crystal.
Thanks
Avril in the Forest UK
____________________________________________________________________________
__
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.
Michael Banks on mon 21 jan 02
Mariko,
The Ceramic Spectrum by Robin Hopper, Published by Krause Publications, 1984
Hardcover, 238 pages; ISBN: 0-8019-7275-2, is one of the best introductory
books on the subject.
If you want to read about Crystal Field Stabilisation Energy Theory, an
authoritative book on the subject is; Burns R.G.: "Mineralogical
Applications of Crystal Field Theory" Cambridge University Press, London
1970. And a web discussion of crystal field theory is to be found at:
http://www.unine.ch/chim/chw/Chapter%204.html
My own approach was via a degree in geology in the 1970's, with emphasis on
igneous petrology and geochemistry. Igneous rocks are very analogous to
glazes. Any knowledge I have of coordination site dynamics in molten
silicate, glasses and crystalline minerals comes from reading publications
in a whole range of periodicals from: the Journal of Geochemical Research
through to Economic Geology.
I got very interested in the parameters controlling octahedral and
tetrahedral sites in silicate liquids while exploring for porphyry copper
deposits in Vietnam and Indonesia in the late 1990's. Copper is only
transported in octahedral sites in magmas and the abundance of these sites
is controlled by the activities of the alkalis and alumina.
As far as I know, there is no mention of the importance of crystal field
stabilisation energy in any ceramic text!! I can't believe that I am the
only person to have noticed this. The applications to the partitioning of
the colouring oxides in zinc crystalline glazes, seem obvious to me....
Michael Banks,
Nelson,
New Zealand
----- Original Message -----
Mariko Cruse wrote:
> I would like to begin educating myself on coloring oxides and other
> glaze-related chemistry. Could you name some currently available text
books
> to start out with? I have some organic chemistry background - such as
> DNA/RNA and antibody detection/production, but practically no experince
with
> inorganic oxides commonly used in this wonderful world of pottery.
Thanking
> you in advance,
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