iandol on mon 3 jul 00
Mica is a natural mineral. There are various species. Muscovite, Biotite =
and Lepidolite are three fairly common ones. They are associated with =
igneous and metamorphic rocks. Muscovite is the one which comes in large =
sheets. One of the most notable deposits is at the Triple Chance Mine =
west of Broken Hill. Muscovite is found in blocks called books. It has a =
quality called cleavage which allows you to split it into thinner and =
thinner sheets but across the sheet it is very strong. Thin sheets, can =
be folded almost double and will spring back again. It is heat resistant =
to a degree but above a certain temperature begins to exfoliate as it =
looses chemical water.Then it becomes vermiculite. I think this is above =
cone 04 because bisque pottery often shows the flash of the flakes. =
Fournier tells us that muscovite mica commences decomposing at 1050 deg =
Celsius forming Mullite and a liquid. This is why it is so useful in =
porcelain and many natural stoneware clays. so it can act as a flux =
which starts to activate below the temperature at which felspar =
activates. Could be useful to the Cone Six Firers. It is also a residual =
mineral in many varieties of kaolin.
Before the advent of all the poly chemicals Muscovite was the most =
important electrical insulator. Large sheets were constructed by =
splitting a book into the finest possible leaves. These were then =
overlaid on a tissue backing. Layers were built up and cemented with =
shellac. =20
I have a mica flour which I used to add to my salt glaze clay body.
Sorry that I have no further information. Read Cardew.
Ivor Lewis. Redhill, South Australia
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