or impossible to use in a clay body, The other common
fluxes, calcium and magnesium, are sudden melters and
are likely to cause instant distortion in the ware
unless the firing is very precisely controlled. Thus
they are better avoided like the plaque, even though
it might seem tempting to bring in some fine-grained
Silica through their silicate forms, wollastonite and
talc, or even wood ash. Bone ash, used in bone china,
is best avoided for the same reason. It is calcium
phosphate, and a sudden melter.

A note on lithium: lithium, the principal flux in
petalite (as well as spodumene, lepidolite, etc.),
is a good supplementary body flux for both glazes and
clay bodies. If used in significant quantities,
however, it might create difficulties because of the
unique physical properties of fired lithium-
silicates. These qualities, which include the
charming contradiction in terms called negative
expansion, are not within the scope of this article.

THE QUARTZ: Additional silica is usually added to
the porcelain in the form of flint or quartz. There
may be some difference in which of them is used
because flint converts more easily to cristobalite
than quartz does, but the main consideration is that
it be extremely finely-ground. (Singer refers to

325 mesh silica as “a fairly coarse form",) The
finer the silica, the better for the glass forming of
porcelain. However finely ground it is, it will have
no more plasticity than wet sand.

Coarse Body Quartz is better left to the formulation
of earthenware and tile bodies, where it is used
largely as a “filler”. not as a source of silica.

Of course, the ideal source of silica is clay and if
the china clays were high enough in silica, there
would be no need for either quartz or flint,

THE BENTONITE: The magic plasticizer. Bentonite

is a clay with an extremely high plasticity and gives
very marked improvement to the workability of a
porcelain body, even at the low but usual addition

of three to five per cent. The additional workability

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