What's Atmospheric Firing?

Kate and Daniel Johnston wood fired Kiln

Kate and Daniel Johnston wood fired Kiln

A lot of times when I’m at the gallery people ask about how different pieces are made, why are certain colors normal for certain firings, what techniques did the artists use, etc.. All this information was new to me as well a few years ago. Fortunately, I’ve developed a wide range of friends with incredible knowledge, background, and experiences in regards to ceramics who have taught me an enormous amount. So, I’ll pass on what I can and find out what I don’t know.

How can you tell when a piece of ceramics has been wood fired?
Starting with the basics; kilns are ovens that heat clay until they go through a chemical and physical change making them hard. One type of kiln firing is something called “Atmospheric Firing”. This means that the atmosphere in the kiln is actually full of chemicals, minerals, etc. that will create glaze on the ceramic work (and everything else in the kiln) without having to actually apply a glaze to the pieces beforehand – think of it as an air-born glaze. There are three basic firing methods that do this;

Wood firing: Andy Palmer, Ashwini Bhat, Justin Lambert, Ken Sedberry, Lindsay Oesterritter, Will Dikert.

Soda firing: Bill Wilkey, Isaac Howard, Zak Helenske.

Salt firing: Kate Johnston, Hitomi Shibata.

Wadding Marks on Justin Lambert plate

Wadding Marks on Justin Lambert plate

Wood firing is when you use wood as your kiln fuel and when the wood combusts it creates ash that’s full of various minerals, metal oxides, chemicals that will actually melt on the ceramics. To prevent the pieces from sticking to the kiln shelves during the firing, little balls of wadding (clay w/ additives) are placed on the shelves and pieces to separate them as they get coated with the wood ash glaze. Many times, and rather traditionally, sea shells were/are used next to the pots on top of the wadding, leaving the sea shell pattern in the glaze. These marks, with or without shells are typical indications of an atmospheric firing.