Janet Kaiser on sun 5 dec 04
Mine was a virulent pink plastic hair roller with quite a large
diameter... Well over an inch as I recall. It was excellent for
quickly scoring slab surfaces or joins. It did not rust, was
easily held with slip-covered hands, would not injure anyone if
left lurking in clay water bowl and would usually float near the
surface so it was never "lost". I used the pink plastic pin (that
pushed through to hold the curler to head) as well... It was a
sturdy "poker". It was a lot larger than the usual brown wire
ones that looked like two legs... They could be used to measure
thickness of freshly thrown pots and were not as painful to
"find" as those lethal pins on wooden handles, which I banished
to the bottom of my tool box after one jammed up under my thumb
nail! It still brings tears to my eyes to recall!!!
As for the question... "WHY do we fire earthenware at a LOWER
temperature in the glost fire?" I have to reply that it is not
always the case, but a "glost firing" is by definition lower than
the biscuit (or bisque) when talking about earthenware or
"china"-- at least it is technically and historically speaking!
Developments in clay and glaze technology, as well as the
introduction of electric kilns in studios over the past 40 years
or so have changed many "traditional" methods as well as
definitions.
When the glost is low (regardless of the biscuit temperature), it
is usually because the glaze being used needs to be fired to a
relatively low temperature. Not only because of the glaze formula
but to retain the colours traditionally used with earthenware,
which would burn out at higher temperatures. However, it is
presumed such a low temperature would not make the clay/body
(especially domestic ware) robust enough to be practical and
would be subject to extreme chipping / breakage during use. We
are very spoiled when it comes to ceramic ware these days... With
it being so extremely robust.. Who remembers vessels where the
rim was a mass of chips, even to the extent of being totally
devoid of all glaze? Not just old stuff in antique shops... New
products with exactly the same properties can still be found in
many tourist destinations... Usually terracotta, or more
accurately Red Ware, which is naturally one reason it fell out of
favour so completely. Often with combed or feathered slip
decoration in black and white on the red ground... "Visit to
Cornwall" ash trays... Must have been millions of them made!
In the case of manufactured china or white ware, the high bisque
is needed to meld the clay into a solid body! I typed out a whole
long post about it some months ago... Giving Dr. Ernst
Rosenthal's wisdom out of "Pottery and Ceramics", so there is a
very detailed account in the Archives somewhere. (Another
occasion where there was never a thank you BTW)
In some low-fired ware, the glaze could even be regarded as an
additional "decoration", all be it a practical way to make it
impervious and hygenic too! The strength and robust nature of the
ware being produced by the biscuit or pre-glaze firing cycle.
At least that is what I was taught a long time ago, "when the
pirates were here" and the mention of L--E--A--D did not shock or
horrify anyone! The firing schedules of "modern" earthenware with
the frits and lead-free glazes on quite different bodies are
quite a different kettle of fish, so the "rule" is no longer hard
and fast AFAIK.
Sincerely
Janet Kaiser - Looking for a kiln to fire around 500 tiles... We
will have to finish Phase II of The Path ourselves... Shame,
isn`t it?
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