I was recently surprised to hear of a fast firing technique called
'wet firing'. With this technique pots are fired 'wet', i.e. they
can be fired straight after throwing and taking off the wheel. Normally
when you try to fire a wet piece, it blows up in the kiln. Why does
clay do this? It has something to do with moisture trying to escape
from the clay too fast. When it can't get out fast enough or evenly
enough, stuff will explode. What can be done about this?
The theory behind wet firing is that if a wet piece is fired in
a kiln atmosphere of high water vapor content, the moisture content
between the inner and outer walls of the clay will be able to equalize,
thus allowing an even, 'soft' escape of the water in the clay.
The high moisture content in the kiln is achieved very simply by
spraying the kiln walls with water before packing/firing. This technique
is suitable for combustion type kilns, e.g. gas kilns, although
if care is taken, it may even be possible in electric kilns. (Please
disconnect power first and use common sense before trying this!)
Because we are talking about firing wet pieces, of course usually
the firing will be a bisque, although there is no reason why once
firings couldn't be done as well.
What this means, is that it is possible to eliminate the fairly
lengthy process of drying a piece from wet to leatherhard to bone
dry before firing -- a considerable saving in time, which can be
crucial to the production potter.
Many thanks to Randy Schmidt, of Arizona State
University for information on the technique of wet firing.
Martha von Redlich
of Hampshire Hill Creations has these comments to share with us:
I have been wet firing poured pieces for years with excellent results.
I do horse models for collectors. I do the original, have the molds
made by a master mold maker, and pour them myself. If I am in a
rush, I slow fire the wet piece, turning up the switches at elongated
lengths of time. Instead of doing the first two when I put the piece
in, I do one switch. Then instead of waiting an hour for the next
switch, I wait two hours, and so on. Logically, it allows the piece
to breathe and let off the water vapor a little at a time as the
kiln warms up and by the time we reach firing temperature, the piece
is ready to fire. Works for me!