David Hendley on sun 20 jan 02
I noticed in the table of available stains that the turquoise stain
I've been using relies on zirconium and vanadium to produce
the color.
This puzzles me, since I've always thought, and every book I've
ever read says, that vanadium in a glaze produces a yellow color.
Has anyone ever made a turquise blue glaze with vanadium
pentoide?
What's going on in with this stain to make turquoise?
It produces a reliable turquoise blue in every slip and glaze I've
tested it in.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
David Hendley on tue 22 jan 02
Thank you very much for your explanation, Michael.
Can you comment on the toxicity of vanadium in the
refractory spinel state, compared to vanadium pentodide?
I've always considered vanadium one of the more toxic
glaze colorants.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "Michael Banks"
To:
Sent: Tuesday, January 22, 2002 10:18 AM
Subject: Re: Zirconium-vanadium turquoise stain
> David,
>
> Commercial ceramic colours are composed of sintered mixtures of two or
> more transition metal oxides. The resultant colour is often unrelated to
> the colours of the original component oxides, or the colours that they
> produce when added to glazes on their own. Many of the compounds are
> refractory spinels, composed of divalent (X) and trivalent (Y) metal ions
in
> the general formula XY2O4. Spinels are refractory and chemically stable
in
> molten glaze, remaining suspended there, so coloured spinels are ideal
> ceramic stains.
>
> The reason why the colours of sintered zirconium-vanadium compounds (in
> turquoise stain), and chrome-tin stains differ from their single
constituent
> oxides, is because in entering the combined molecule one or both of the
> metal ions is forced into a lower valency state than we are used to
> encountering in glazes.
>
> E.G: In chromium-tin stain, the normally green chromic (III) ion is forced
> to reduce to the chromous (II) ion which is ruby red in colour. Normally
> (on it's own) Cr (III) is too stable to reduce to Cr (II) and yield a red
> colour in glaze. I believe a similar mechanism operates in
> vanadium-zirconium stain, the turquoise colour coming vanadium reduced to
a
> lower valency value than the pentavalent (V5+) ion (yellow-brown) normally
> seen in glazes.
>
> Michael Banks,
> Nelson,
> New Zealand
>
> ----- Original Message -----
> From: David Hendley wrote:
> > I noticed in the table of available stains that the turquoise stain
> > I've been using relies on zirconium and vanadium to produce
> > the color.
> > This puzzles me, since I've always thought, and every book I've
> > ever read says, that vanadium in a glaze produces a yellow color.
Michael Banks on wed 23 jan 02
I think that the Zr-V stains (turquoise, chartreuse, lime green, "celadon
green etc) are regarded as having low solubility and low-toxicity. But
check with the manufacturers (Cerdec, Degussa etc).
Spinels generally are very hard and chemically durable with Moh hardnesses
in the 7-8 range.
Natural spinels: magnetite (Fe:Fe), gahnite (Zn:Al), spinel (Mg:Al),
chromite (Fe:Cr), hercynite (Fe:Al), galaxite (Mn:Al), trevorite (Ni:Fe)
etc, can occur as heavy detrital minerals in beach sands and other
sediments. This is, because they are so insoluble and chemically stable that
they survive the millions of years of weathering, that have destroyed their
original host rocks.
Michael
NZ
----- Original Message -----
David Hendley wrote:
> Can you comment on the toxicity of vanadium in the
> refractory spinel state, compared to vanadium pentodide?
> I've always considered vanadium one of the more toxic
> glaze colorants.
Michael Banks on wed 23 jan 02
David,
Commercial ceramic colours are composed of sintered mixtures of two or
more transition metal oxides. The resultant colour is often unrelated to
the colours of the original component oxides, or the colours that they
produce when added to glazes on their own. Many of the compounds are
refractory spinels, composed of divalent (X) and trivalent (Y) metal ions in
the general formula XY2O4. Spinels are refractory and chemically stable in
molten glaze, remaining suspended there, so coloured spinels are ideal
ceramic stains.
The reason why the colours of sintered zirconium-vanadium compounds (in
turquoise stain), and chrome-tin stains differ from their single constituent
oxides, is because in entering the combined molecule one or both of the
metal ions is forced into a lower valency state than we are used to
encountering in glazes.
E.G: In chromium-tin stain, the normally green chromic (III) ion is forced
to reduce to the chromous (II) ion which is ruby red in colour. Normally
(on it's own) Cr (III) is too stable to reduce to Cr (II) and yield a red
colour in glaze. I believe a similar mechanism operates in
vanadium-zirconium stain, the turquoise colour coming vanadium reduced to a
lower valency value than the pentavalent (V5+) ion (yellow-brown) normally
seen in glazes.
Michael Banks,
Nelson,
New Zealand
----- Original Message -----
From: David Hendley wrote:
> I noticed in the table of available stains that the turquoise stain
> I've been using relies on zirconium and vanadium to produce
> the color.
> This puzzles me, since I've always thought, and every book I've
> ever read says, that vanadium in a glaze produces a yellow color.
> Has anyone ever made a turquise blue glaze with vanadium
> pentoide?
> What's going on in with this stain to make turquoise?
> It produces a reliable turquoise blue in every slip and glaze I've
> tested it in.
Paul Lewing on wed 23 jan 02
Actually, I have two questions on this subject.
The first is that Hamer and Hamer say that a spinel is a combination of an
alkali and an amphoteric that acts like an acid. They give examples of
Co/Al, Mg/Al, and so on. But isn't ZrO2 an acid itself? And which is V2O5?
The second (and I believe David originally asked this as well, is, does the
formation of a blue color from a V/Zr spinel require the same kind of
particular glaze chemistry and exacting proportions that a Cr/Sn pink
requires? If so, what are the requirements, and can you make one yourself
from V2O5 and ZrO2, or do you need to use a prepared stain?
Paul Lewing, Seattle,
eagerly awaiting another great Michael Banks lesson.
iandol on thu 24 jan 02
Dear Paul Lewing,
I think the relationships between transition elements and colour in =
ceramic glazes and stains is a bit more complex than the chemistry given =
in Hamer and Hamer, something to do with the electron conformation of =
something known as the 3d and 4f electron bands. I have been trying to =
get my head around the Vanadium question and it is complex. It seems the =
blue has something to do with Vanadium Dioxide, a chemical we are not =
familiar with. In addition, Vanadium is an element which has a lot of =
oxides.
There is also a lot about colour which is tied up with the reaction and =
formation of molecular structures in glasses. It also seems to depend =
on the presence or absence of a variety of interstitial defects, that is =
electrons or electron holes (Please don't ask!!), substitutions in solid =
solutions (Cr in Red Corundum as an example)and other sorts of vacancies =
and substitutions in lattice structures which have an ability to react =
with photons to give either adsorption or emission colours.
Vanadium Pentoxide is reported to be amphoteric as can Ferric Oxide be. =
These give rise to Vanadates and Ferrites. So presumabley the blue stain =
can be a Zirconium Vanadate, which I believe we are told, has a Spinel =
structure, though I am not sure if this means that it qualifies to be a =
spinel.
I am a bit suspicious about these labels of acid, base and amphoteric as =
ways of explaining things which are happening at highly elevated =
temperatures. I begin to wonder which definitions are being used, high =
school ones where a salt is being formed or industrial ones, as in Basic =
Open Hearth or Acid Open Hearth furnaces (Do they still exist??).
Yes, It is a good job we have Michael Banks in there batting for our =
side. His recent posts have ben highly enlightening.
All the best.
Ivor Lewis. Redhill, South Australia.
Michael Banks on thu 24 jan 02
I don't know the answer to your first question Paul. Are "acid, alkali and
amphoteric" still valid concepts in regard to transition metal oxide
reactions? Crystal field stabilisation energies are currently thought to
govern entry of these cations into complex oxides.
To the second question: Yes.
Singer & Singer give the following recipe for "turkish blue" Zr-V stain (%):
barium carbonate 8.5
vanadic acid hydrate 12.5
zirconium oxide 48
silica 31
Wet grind, dry, calcine at cone 5-7. Stable in glaze fired cones 6-9. Not
recommended for low temperatures.
Formation of vanadium blues (V4+ ion) in a standard glaze does not seem too
likely, given the refractory nature of the amounts of zirconium oxide
required above.
Michael
----- Original Message -----
Paul Lewing wrote:
> Actually, I have two questions on this subject.
> The first is that Hamer and Hamer say that a spinel is a combination of an
> alkali and an amphoteric that acts like an acid. They give examples of
> Co/Al, Mg/Al, and so on. But isn't ZrO2 an acid itself? And which is
V2O5?
> The second (and I believe David originally asked this as well, is, does
the
> formation of a blue color from a V/Zr spinel require the same kind of
> particular glaze chemistry and exacting proportions that a Cr/Sn pink
> requires? If so, what are the requirements, and can you make one yourself
> from V2O5 and ZrO2, or do you need to use a prepared stain?
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