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terra sig australia

updated fri 22 jan 99


Michael Banks on tue 19 jan 99

A couple of probable reasons for the lack of sheen in your white terra sig
is the presence of the frits and that the Clay Ceram base may not be
suitable for the purpose.

A good terra sig is not a glaze and should not need any accessory fluxes.
The ultra fine clay fraction (which terra sig is composed of) should sinter
naturally like the underlying clay body. Sintering is a process where the
clay crystals stick to one another at their edges. It doesn't distrupt the
reflective flat faces of the crystals which is what you're relying on to
produce the sheen. Aggressive fluxes such as frits, attack these reflective
surfaces and disrupt them. Melting is inimical to terra sig. Actually, I
think 1080 is a bit on the hot side for a good terra sig.

While I haven't tried clay ceram as a base for terra sig, if it's not
working, even after removing the frit, I would try a platy kaolin instead of
a plastic ball clay in future. Clay ceram is a superb plastic ball clay,
but is quite high in free silica which tends to dilute the sheen.

Platy kaolins are often not plastic but are rich in crystalline kaolinite,
even down at the very fine fraction. Kaolin crystals are what you're after.
China clays (kaolins) which are used in the paper coating industry are a
good choice for white terra sig, because glossy paper is virtually unfired
terra siggillata! Paper coating kaolins are also very pure, are maximised
for fine grainsize and are usually quartz-free.

Hope this helps,

Michael Banks
New Zealand

-----Original Message----abridged-
>I am currently working on developing a white terra sigilatta......results
have shown no sheen.........

John K. Dellow on wed 20 jan 99

According to my 1978 Geological Survey of Kaolin in New South Wales Australia.
"Eckacote & Pittong Filler " would fall into the parameters given by Michael

John Dellow "the flower pot man"
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