John Sankey on wed 12 sep 07
I've had a breakthrough with my investigation of iron glazes.
After inquiries to several local government departments, museums
etc. dealing with minerals, I clicked with one!
John Stirling, who works in the research labs of our venerable
Geological Survey of Canada, was intrigued by the possible
minerals in my samples. He uses a scanning electron microscope
(a very modern version of the one I used for my postgraduate work
to study microwave cathodes), but has it coupled to a modern X-
ray analyser that can determine some of the composition of what
the SEM sees (the elements heavier than sodium).
The results are summarized on my iron glaze page
http://sankey.ws/glazeiron.html
and show just how differentiated (chemically messy) a borate-iron
glaze is and, by contrast, how chemically simple reliable iron
glazes are.
My next step is to study the substitution of lithium for potash
to control expansion rate of the best red glaze I've found, to
ensure that it is as reliable as the version I have now. (No use
going back to the lab with it; lithium is too light for the GSC
analyser to detect.)
Neal on thu 13 sep 07
After the article about iron reds in Ceramics
Monthly, I changed my firing schedule for the
last two kiln loads. It's now going through a
fast cooling from 2000 to 1700, holding for
15 minutes, then an hour down to 1650, holding
for 15 minutes, and an hour down to 1600. (Or
for those who think in Celsius, fast cooling
from about 1100 to 930, 15-minute hold, two
hours down to 870 with a 15-minute hold at 900.)
My photo of the eclipse plate detail shows the
iron red glaze fired with this schedule:
http://www.flickr.com/photos/clayart/
I'm happy with the way that glaze is turning
out consistently now. Before I had much greater
variation between pieces in the same kiln load.
Neal O'Briant
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