Understanding the Flow of the Flame in a Wood/Soda Firing

Learn how to get beautiful wood-firing results!

wood firing

In soda, salt, and wood firing, understanding the flow of the flame is crucial to getting good results out of the kiln. So potters like Stuart Gair put a lot of thought into how they load pots into their kilns. And you can tell in the finished work. 

In today’s post, an excerpt from the April 2021 issue of Ceramics Monthly, Stuart explains how he observes the flame path in his wood firings, and then uses those observations to create diagrams of how to place his pots. He also talks about the materials he uses for wadding his pots and how they impact his results. –Jennifer Poellot Harnetty, editor.


Flow of the Flames

It’s also important to understand how the flame moves through the specific kiln being fired. This can be done by pulling peep bricks and watching the flame throughout the firing. It has helped me to draw diagrams of the kiln with winding arrows pointing in the different directions that the flame is moving. This is easily accomplished and really helps when loading the kiln and trying to anticipate the way that the flame is flowing. Pots and bricks can be used to direct the flame to different areas of the kiln or toward other pots. The envelope vases work great for this.

Wood Kiln Firing Techniques and Tips

Learn the fundamentals for wood kiln firing when you download this freebieWood Kiln Firing Techniques and Tips.



 

Typically, I place pots in such a way that the flame and soda can reach all of the pots. On each shelf, taller pots are positioned in the middle and they taper in size toward the shelf’s edge where the smallest pots are placed, allowing the flame to reach pots that are normally hidden or blocked. I’ve also found that this approach to stacking helps the flame move more freely through the chamber, making it easier to make adjustments in order to fire the kiln more evenly top to bottom, particularly earlier in the firing.

1 Iron-rich wads are also placed in between pieces in anticipation of the path of the flame in order to create particular protected marks.

2 Iron-rich wads are also placed in between pieces in anticipation of the path of the flame in order to create particular protected marks.

3 The back stack is loaded first.

I like comparing the flow of the flame to that of a river. The main flame flows from the burners, through the chamber, and eventually out the flue. In addition to that primary flame, there are also a number of smaller paths, like tributaries, that flow to different parts of the kiln and may create hot and cold pockets, which are helpful to identify. Like a river, constricted areas create a higher flow velocity and more dramatic marks on the wares than areas where the flow is open and slow.

Materials and Firing the Kiln

Materials are important to consider before firing a soda kiln. Using clays or slips that will accept more soda than others results in shiny surfaces. Conversely, a matte surface comes from the use of materials that are more refractory. Some materials encourage flashing while others are more uniform, subdued, and muted. Lighter clays and slips tend to yield a spectrum of lighter and brighter colors such as pinks, yellows, oranges, and grays. Clays with more iron may produce darker hues of brown, navy, orange, maroon, or gray. The key here is testing and always having tests in each firing. Currently, I’m exploring applying light slips over dark clays and dark slips over light clays to achieve more depth in the surface. Once you become more familiar with the kiln you’re firing, you may begin to understand what slips and glazes work best in particular areas of the kiln. I typically have around five different slips, glazes, and clays placed in different zones of the kiln where they are most suitable.

4 Pots are positioned to create good airflow and an opportunity for the soda and flame to reach each piece.

5 High-alumina wadding is placed between posts and shelves.

Finally, the firing of the kiln is an important factor that can dramatically alter the outcome of the surface and color of the wares inside. Firing in a reduced atmosphere (more fuel than air) versus an oxidized atmosphere may be the difference between a clay coming out orange or gray. It may also be the difference between a glaze turning out red or blue. I typically fire the kiln in both oxidation and reduction cycles throughout the firing. Reducing the kiln early affects the color of the clays I use, and reducing the kiln late in the firing affects the color of my glazes.

The forefront of my research has been the importance of reduction and oxidation cycles at the end of the firing, as well as oxidation cooling. While spraying a combination of dissolved soda ash and water at the end of the firing, I simultaneously experiment with oxidation and reduction cycles, almost like the kiln is inhaling and exhaling. After the soda mixture is sprayed into the kiln as quickly as possible and the oxidation/reduction cycles are complete, the kiln is turned off and quickly cooled in a process I call oxidation cooling, an idea that originated from pulling draw rings from the kiln. In order to introduce as much oxygen as quickly as possible into the kiln, all of the peep bricks are opened, fans are left on, and the door is cracked opened, if possible, and an additional fan is directed toward the stack. This fast re-oxidation brings out a much greater range of color and subtleties that would otherwise be lost. Please don’t try this method unless you have taken all of the safety precautions and are using a kiln in a fireproof setting.

The ultimate resource for low temperature soda firing!

Justin Rothshank's Low-Fire Soda is a start-to-finish resource on soda firing at low temperatures—from the different types of clay bodies to use, to decorating and glazing techniques, wadding and loading strategies, firing tips, post-firing ideas, and much more. Whether you’re interested in learning about faster, more economical atmospheric firings, or you’re intrigued by the expanded color palette of low-fire clay materials, Low-Fire Soda has the information you need to start exploring low-temperature atmospheric firings.

Read an excerpt!

Soda firing continues to keep my full attention and is really exciting to me because it’s a relatively new approach (originating in the 1970s) to firing ceramics and it seems like artists who soda fire are discovering new techniques and experiments to try every day.

the author Stuart Gair has a BA in history from Ohio University, and completed the M.Ed. program at John Carroll University in Ohio, along with the post-baccalaureate programs at Ohio University and the University of Nebraska-Lincoln. He earned an MFA in ceramics from the University of Nebraska-Lincoln. He was a resident artist at the Archie Bray Foundation for the Ceramic Arts in Helena, Montana, and Watershed Center for the Ceramic Arts in Newcastle, Maine. To learn more, visit http://stuartgair.com.

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