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Firing
The completely dry pot, now called greenware, is still quite fragile. If
handled roughly, it can easily chip or break. If water is added to it, the
piece will soften and become clay again. It must be fired if it is
to become a useful vessel.
The first firing is the bisque (or biscuit) firing. Since no glaze is
applied at this time, pots may be stacked or placed inside each other in the
kiln. After the kiln is loaded, the lid is propped open a couple inches,
then turned on low overnight, warming the ware slowly. The lid is then
closed and the temperature raised to over 1800˚ F. During this process,
all the remaining water is driven off and the clay changes to porous "stone"
which holds its shape but still chips easily and is not very durable.
Bisque ware absorbs water, but does not return to workable clay due to the
chemical changes which occurred during the firing. When the firing is
complete, the kiln is allowed to cool before it is unloaded.
Before glazing, bisque pieces are wiped with a damp cloth to remove any dust
which may interfere with the glaze adhering to the pot. To prevent the pot
from sticking to the shelf during the final firing, the foot ring is waxed
before it is glazed and any droplets of glaze are wiped off before the pot goes
into the kiln.
The many options for decorating the pot at this point include painting an
underglaze design
before glaze is applied,
layering different glazes, and brushing stains over the glaze. Different
glazes chemically interact during the glaze firing, often producing interesting
effects. Glaze may be applied by pouring, brushing, or spraying, or the
pot may be dipped in the glaze. One to three coats of glaze may be
applied, and all coats may be of the same or different glazes.
Once the glaze dries, the pot must be handled with care so as to avoid chipping
the glaze off the pot or otherwise damaging it. Pots are now loaded into
the kiln again, leaving at least 1/2" between pieces. Pieces which touch
in this firing will be "glued" to each other permanently! The kiln is
fired to a final temperature of about 2200˚
degrees F. During this firing, the clay matures to dense stone and the
glaze chemically bonds with the clay. The kiln is allowed to cool until
the pots can be handled with bare hands, approximately 120˚F, and then it is
unloaded. Each piece is inspected and any rough spots on the foot ring are
smoothed off.
The journey is now complete! The lump of clay we started with has now
become a finished usable piece. The glazed ware is durable,
chip-resistant, and waterproof... and it is beautiful!
The Process Clay and Glazes Throwing Trimming
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