John Sankey on sat 5 may 07
-Very technical; much of the book focuses on decoloring impure
glasses, avoiding opacifiers, and the use of toxic materials
such as lead, cadmium and uranium. This is what I think might be
useful to a potter:
-Beer's Law: absorption of colorant is proportional to
concentration. Not followed closely by some dilute ions.
-Glass types: soda-lime-silicate, borosilicate, lead; behaviour
of colorants varies between them.
-Some ions produce different colours depending on whether they
act as network formers (the equivalent of taking part in a
crystal lattice) or network modifiers (equivalent of
interstitial atoms in crystals).
-Iron: can be divalent (FeO black oxide) or trivalent (Fe2O3 red
oxide). FeO can produce light blue in strongly reducing glasses,
but both normally produce red-brown. Phosphates can modify this
to a pink. Iron has lightest colour in potash glasses, darker in
soda, darkest with lithia.
-Manganese: trivalent is purple, shifts from red to blue as the
alkali shifts from lithia to potash; most is divalent, weak
yellow to brown; MnO2 main effect is as oxidizer for iron etc.
-Chromium: name chromos means many colours. Cr2O3 is immiscible
in silica so precipitates in excess; volatile above ^04. In
acidic glasses, green when thin, shifting to blue even red when
thick; dichromate yellow green, trichromate emerald green; borax
increases chromium colours; chromium-tin is pink, chromium-zinc
brown.
-Copper: Cupric CuO light blue at low temperature soda glass,
green in borosilicate high temp. Cuprous colourless by itself
but intensifies cupric colours. Borax shifts blue to green, so
does titania; volatile above ^03.
-Cobalt: blue, purer colour with potash than with soda or lithia.
-Nickel: grey, even absorption, slightly on brown side.
-Titania (rutile): essentially colourless but affects other
colours; iron moves from green to brown because iron is moved
from network-modifying role to network forming. Copper changes
from blue to green even brown when this occurs.
-Vanadium: with tin is cream yellow; with zircon turquoise.
-Cerium: faintly yellow, unstable.
-Praseodymium: yellow
-Selenium: volatile; cadmium sulphide+selenium in potash glasses
is fire red; makes good black with cobalt.
-Tin: very little understood.
-Metals (e.g.gold) in glasses are colloidal (hundreds of atoms in
a clump) not dissolved.
Timothy Joko-Veltman on sat 5 may 07
John,
Thank you for the summary.
As for volatility, many books/websites refer to chrome oxide's
volatility above 1200C. Is it then less volatile in a glaze than in a
glass? What about copper? Does it also volatilize in glazes from
^03?
Regards,
Tim
Ron Roy on thu 10 may 07
Hi Tim,
The testing I have done indicates it is volatile even at cone 04.
RR
On 5-May-07, at 12:51 PM, Timothy Joko-Veltman wrote:
> John,
>
> Thank you for the summary.
>
> As for volatility, many books/websites refer to chrome oxide's
> volatility above 1200C. Is it then less volatile in a glaze than in a
> glass? What about copper? Does it also volatilize in glazes from
> ^03?
>
> Regards,
>
> Tim
>
Timothy Joko-Veltman on fri 11 may 07
Ron,
Is that for chrome or copper?
Tim
On 5/10/07, Ron Roy wrote:
> Hi Tim,
>
> The testing I have done indicates it is volatile even at cone 04.
>
> RR
>
>
> On 5-May-07, at 12:51 PM, Timothy Joko-Veltman wrote:
>
> > John,
> >
> > Thank you for the summary.
> >
> > As for volatility, many books/websites refer to chrome oxide's
> > volatility above 1200C. Is it then less volatile in a glaze than in a
> > glass? What about copper? Does it also volatilize in glazes from
> > ^03?
> >
> > Regards,
> >
> > Tim
> >
>
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Dan Semler on fri 11 may 07
Hi Ron, Tim, All,
I found an interesting paper today which I checked out in the =20
Literature Abstracts on Ceramic Glazes. Its full citation is :
Journal of the American Ceramic Society
Volume 23 Issue 4 Page 111 - April 1940
To cite this article: H. C. Harrison, W. G. Lawrence, D. J. Tucker? (1940)
AN INVESTIGATION OF THE VOLATILITY OF GLAZE CONSTITUENTS BY THE USE OF =20
THE SPECTROGRAPH*
Journal of the American Ceramic Society 23 (4), 111?116.
Anyhow, I will probably try to get my library to get it, but there is =20
an interesting summary of it in the Abstracts.
I'll quote the second par which seems most relevant :
"The temperature at which boron, lead and chromium oxides start to =20
volatilize from a cone 04 glaze was studied and found to be : =20
boron-450, lead-850 and chromium-1000 deg C. The effect of soaking =20
heat was found to give an increased concentration of the volatile =20
constituents even after the muffle had started to cool. An increase in =20
the silica content of the cone 04 glaze increased the volatilization =20
temperatures of boron, lead and chromium oxides. In the case of a high =20
calcium glaze in which B2O3 and part of the PbO were introduced in the =20
fritted portion, the B2O3 was less volatile at all temperatures that =20
when it was introduced as colemanite or as B2O3, but the =20
volatilization temperature of PbO was lowered."
Thanx
D
Ivor and Olive Lewis on mon 14 may 07
Dear Dan Semler,.
Will ask the library if they can get me an off print of that report.
If a Spectrophotometer was used then there should be quantitative as =
well as qualitative information.
Thanks for doing the digging.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on mon 14 may 07
Hi Tim,
I have not tested copper or manganese at any temperature - just chrome at
cone 04 and 6.
RR
>Ron,
>
>Is that for chrome or copper?
>
>Tim
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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