Janet H Walker on tue 19 nov 96
I was reading a fairly technical book recently (a hobby of mine,
reading stuff that I don't understand, kinda like "pumping iron"
for the brain; no pain, no gain...) Anyhow, in the discussion on
what happens to glazes during firing, the author was talking about
things that happen on the glaze surface that can affect appearance.
"Another cause [of changes in appearance] is the presence of gases
or vapours in the kiln atmosphere that react with the glaze surface.
When sulphur-containing fuels are used, the sulphates in the gases
can be taken into solution by the glaze. If saturation is reached,
crystallization will take place during the cooling, giving the
well-known 'sulphuring' or 'feathering' fault."
(From Dinsdale, Pottery Science, 1986)
My copy of Hamer is elsewhere so I can't look up "sulphuring" but I
don't remember hearing this term. Is this just "well known" in
industrial type situations where they might be firing with oil (or
coal!)? or can it happen with gas fired kilns? I'm not familiar
with contaminant levels in gas but I assume there's more in there
than just the gas. Anyone happen to know about this from
experience? Thanks for satisfying my curiosity.
Jan Walker
Cambridge MA USA
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