The
purposes of these two types of kiln differ, so insulation properties
differ too. Ceramic kilns have high density brick insulation to
retain the heat and slowly cool the contents from the top temperature
to avoid breakage. Glass kilns have light weight insulation –
whether brick or fibre - to cool quickly from the top temperature to
avoid devitrification.
Considerations
Controllers
are necessary for controlled soaks and cooling on glass kilns. Much
simpler controls are sufficient for ceramics firings. So a ceramics
kiln needs to have a controller added. This is a significant cost.
If buying a ceramics kiln new for glass work, ensure it has a
controller that can be used for glass.
Heat
distribution
is different in the two. Glass kilns are shallow to get even heat
distribution to the surface of the glass. Ceramic kilns have
elements around the sides and frequently in the top, but may not have
any in the door, if it is not top loading. This means the heat
distribution in a ceramic kiln is not as even as in a glass kiln,
which is not a problem for ceramics as so much heat is retained at
the target temperature, it equalises as the kiln cools.
Loading
Ceramic
kilns up to 450 mm deep tend to be top loading, the ones with greater
depth tend to have doors. Glass kilns are shallower and tend to have
top – just the lid opens - , clamshell – the lid is the whole
chamber which opens giving direct access to the floor of the kiln -
or bell type – where the lid also forming the chamber is lifted
from the base of the kiln and often the base is on wheels so another
base of prepared work can be wheeled into place for firing before the
kiln has completely cooled.
Baffles
are required in ceramic kilns because the heat is greater nearer the
elements on the initial advance in temperature. These baffles avoid
premature sealing of the edges of pieces causing large bubbles.
Firing
on multiple
levels is
possible in ceramic once you have built up the experience.
Schedules
have to take into account the greater mass of insulation in ceramic
kilns.
Annealing
and cooling
tends to require different strategies to encourage the ceramics kiln
to cool fast enough in the devitrification range, but can have the
power turned off earlier after the annealing soak, because of the
slower cooling.
Ceramic
kilns are ideal for casting.
Cost
– ceramic kilns tend to cost less than glass ones and second hand
ones have been more widely available. That may be changing now with
the increasing popularity of glass fusing.
The electricity costs are marginally higher in ceramic kilns than glass, because the mass of brick to be heated up is greater..
The electricity costs are marginally higher in ceramic kilns than glass, because the mass of brick to be heated up is greater..
Space
-
Ceramic kilns tend to take up less floor space because they are deep
or tall rather than broad.
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