High Bisque, Low Glaze
normal way for the studio potter to fire ceramics is usually to
bisque the wares to somewhere between cone 09 and cone 06 (-- explanation
of cone temperatures), glaze the work and then fire to the
maturation temperature of the clay body and the glaze. This would
go for earthenware as well as stoneware. However there is another
method to fire ceramics, and that is a technique often used in industry,
where the ceramics are bisqued to a higher temperature than the
This works best with earthenware or midfire clays bodies, as they
are still somewhat porous when high fired. This means that they
still have the capacity to soak up the glaze. A typical combination
might be to bisque to cone 01 and then glaze fire the work to cone
There are a couple of things that need to be taken into consideration.
First of all, the clay should be strong enough for your needs after
the bisque firing, as the subsequent lower temperature glaze firing
will not further vitrify the clay much, if at all. Secondly, the
lower fire glaze should be tested for a good glaze fit. This is
not automatically guaranteed and the usual problems of crazing or
shivering or pinholing can still occur, so previous testing is paramount.
Underglaze decoration can still be done on greenware or bisque.
The technique is less suited to stoneware or porcelain although
not impossible. The problem is that the higher fired ware has become
vitreous, so it won't soak up any glaze. This excludes the normal
methods of glazing such as dipping or under normal circumstances
spraying. To overcome this problem, the vitrified work needs to
be heated with a burner, then a light coat of glaze is sprayed on.
The process is repeated until a sufficient layer of glaze has built
up. The thickness of the glaze may need to be tested by scratching
it with a pin or nail. In this case, it is also recommended to put
some gum arabic or CMC into the glaze to stop it brushing of when
handling to put in the kiln. In some cases, this technique will
be desirable even for stoneware or porcelain, especially when applying
glaze to bisque ware somehow influences the decoration, as would
be the case with water-soluble metal salts.