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Wet Firing

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!

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