Jim Murphy on tue 15 apr 03
Hi Ivor,
At the risk of being completely and totally off the mark, I'll venture a
guess on the yellow crystals and slight optical blue.
on 4/14/03 11:39 PM, iandol at iandol@TELL.NET.AU wrote:
=20
> Next to hand were the line blends using Mintaro Slate Powder.
> The high Slate/Ash samples gave an observation which was completely
> unexpected. The 70/30 and 80/20 Slate/Ash samples developed sulphur yello=
w
> crystals. Some of these are in florets, others are blades. The 90/10 and =
100%
> samples also gave crystals, duller, darker and smaller. It is interesting=
to
> note that the 90/10 and 100% slate samples on the other three tiles also =
show
> clear signs of crystal segregation over a substrate which has melted
> completely to a black glass.
The 3 tiles with 90/10 and 100% slate that formed a black glass substrate
may imply the slate itself forms a low alumina alkaline or feldspathic glaz=
e
- like a Tenmoku glaze with heavy Iron Oxide content. The yellow crystals
more developed in the 70/30 and 80/20 Slate/Ash samples may imply the
production of pyroxene crystals possibly due to MgO (from the ash) and Iron
Oxide. A similar result is seen - yellow "teadust" crystals formed - when a
Magnesia glaze combines with a Tenmoku glaze.=A0
=20
> Another clue comes from two 6*6 tiles, one with washed ash, the
> other with raw ash. Several samples on each tile in the same region show
> slight optical blue, taking the obvious reduced Iron green towards the
> aquamarine. I already have ideas but other opinions would be appreciated.
Is it possible the blue color is formed due to P2O5 supplied from fruitwood
in your mixed ash ? Hank Morrow has noted a "Chun" soft blue may form with
small additions of phosphorus to a limestone glaze with low amounts of Iron=
.
Please refrain from having an aneurysm if my guess makes no sense at all.
=20
> But later I will be analysing the
> Wollastonite-Kaolin-Silica-K-Felspar series in the hope of building a 3D =
plot.
Keep us posted on this series and the 3D plot.
Thanks,
Jim Murphy
iandol on tue 15 apr 03
Dear Friends,
To take almost three hundred samples from the kiln was a delight. Six =
superb 6*6 tiles and four line blends plus a repeat firing of the high =
Barium 6*6 tile
One of the first things I wanted to see was if the series with up to 24% =
Barium Carbonate was firing consistently. It was. Samples with low =
values tended to be opaque, those with high values were transparent. I'm =
not sure it would be worth the effort of cutting the samples out and =
crushing them to do water and acid extractions.=20
Next to hand were the line blends using Mintaro Slate Powder. This had =
been line blended with Soda Felspar, Potash Felspar, Nepheline Syenite =
and Mixed Ash. Since there is a consensus that high Soda fluxed glazes =
tend to craze whereas Potash fluxed glazes are less prone to this fault =
I might have predicted that there would be little or no crazing with the =
K-felspar, some crazing with the Neph. Sy. and well crazed specimens =
with Soda Felspar. Well, There was considerable crazing down the line =
with Neph Sy and several samples with crazing with K-Felspar. Five =
samples on the Ash rich side of the Ash Slate series crazed as well. =
Only the pure Na Felspar sample crazed in that series. This seems to be =
an anomalous result
The high Slate/Ash samples gave an observation which was completely =
unexpected. The 70/30 and 80/20 Slate/Ash samples developed sulphur =
yellow crystals. Some of these are in florets, others are blades. The =
90/10 and 100% samples also gave crystals, duller, darker and smaller. =
It is interesting to note that the 90/10 and 100% slate samples on the =
other three tiles also show clear signs of crystal segregation over a =
substrate which has melted completely to a black glass. Given that Slate =
is a partially metamorphosed clay then there might be some speculation =
as to the origins of these artefacts. Another clue comes from two 6*6 =
tiles, one with washed ash, the other with raw ash. Several samples on =
each tile in the same region show slight optical blue, taking the =
obvious reduced Iron green towards the aquamarine. I already have ideas =
but other opinions would be appreciated.=20
Sorry folks, I have no analyses for the ashes or the slate so computer =
analysis will not be of much use. But later I will be analysing the =
Wollastonite-Kaolin-Silica-K-Felspar series in the hope of building a 3D =
plot.
Best regards,
Ivor Lewis. Redhill, South Australia.
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