and carefully raise the feldspar content. A rough
method, it is a perfectly workable one, and has the
advantage of matching the available materials and the
existing firing cycle to the recipe.

Assuming that the porcelain recipe is nearly right,
with approximately the right balance of silica,
alumina and fluxes, and that the glaze or glazes are
themselves well-balanced, a long firing with fine
silica will result in the maximum silica glass and the
highest degree of vitrification and translucency. If
crazing occurs. the recipe calls for: more silica for
better fit but likely loss of vitrification and
translucency (commonly called "V and T") or finer
silica or longer firing for better fit-maintaining or
gaining in V and T.

If it shivers (or spiral-—cracks, or shatters), it
needs: less silica for better fit with gain of V and T
or coarser silica or shorter firing for better fit with
loss of V and T.

NOTE: the addition of feldspar, often advised as a

cure for shivering, etc. will work on’y if the body

is already underfluxed. Thus it often works well in
stoneware bodies, but in porcelain is more likely to
cause a sharp increase in distortion.

To put the same kind of information the other way
around: assuming that the porcelain recipe is nearly
right, etc. the following are the likely symptoms
resulting from:

TOO MUCH CHINA CLAY - lowered V and T, a tendency
toward dull qualities in both body and glazes.

TOO MUCH SILICA - less V and T, dry surface, sugary
look, tendency toward shivering.

TOO MUCH FELDSPAR - Slumping or over-distortion very
glassy, tendency toward crazing.

TWO PORCELAIN GLAZES

Here are two recipes for “conventional” well-fitting
porcelain glazes which will fire between cone & and
10 in most kiln cycles, producing smooth, bright
glazes. The first is Salvetat's Modern Chinese

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