All of the analyses will produce vitrified, trans-
lucent porcelain between cone 8 and cone 10. In
descending order from (a) to {e) they will be more
plastic and workable but less vitreous and translucent
with more inclination toward crazing unless they are
fired very slowly. Thus the working properties and
the fired qualities are in some opposition to one
another, and it is quite true to say that the more
ae the porcelain body the longer it must be

red.

It is a fairly simple matter with a slide-rule to cal-
culate recipes to fit these analyses. A little
variation in the silica content will make little
difference, It is unlikely that you will achieve a
body that can be thrown with ease unless you include
two to five per cent bentonite in every recipe. To
diversify the fluxes by using a number of different
feldspars and alumino-silicates will likely improve
the fluxing of the body, but as most are higher in
alumina than feldspar (relative to the fluxes) they
will also diminish the quantity of clay in the recipe.
Above all things, use the finest-grained silica which
you can obtain and soak the firing as. long as you can
endure. If you use simple, clear, transparent por-
celain glazes they will bring out the best qualities.
If the body has a high degree of translucency it is
Surprising just how glazes can be which are at the
Same time highly coloured. It is not colour which
makes glazes opaque.

MAKING A PORCELAIN BODY: EMPIRICAL MEANS

If the chemistry makes you nervous, a porcelain clay
body can be made by empiral means. As a beginning,
take this recipe: 50 China Clay, 25 Felspar, 15
Quartz, 5 Bentonite. Fire it. It is quite low in
silica and the glazes will likely craze. If they do,
increase the quartz in the body until the glazes

Fit. The recipe will be unlikely to take more than
29 parts quartz. If the firing cycle is short, so
much quartz may be needed that the fired body will
begin to look "dry" and plaster-like, although the
body may be translucent. This is an indication that
the recipe has run out of fluxes, and you must slowly

ee