An ongoing investigation of the soda-firing process continues to provide new surprises and facilitate new avenues of exploration. A common misunderstanding of the process is that it is random and putting a piece into an atmospheric kiln is the equivalent of passing that piece “on to the kiln gods.” One of the most important things I have learned about this particular process is that most of the work goes into preparedness before lighting the burners and being able to anticipate the final outcome as much as possible. Particular attention is given to form, materials, placement, and the way in which the kiln is fired.
Form and Interaction
The form of each piece plays a crucial role in how the soda and flame interact with it. Spherical shapes encourage the flame to wrap around them and oftentimes accentuate their form, depending on where they are placed in the kiln. Surface results tend to be subtle on a spherical shape and show gradation in tone, hue, and sheen because of both the way they record the flame path from all directions and the angle at which the form meets the shelf. Angular or rigid forms respond very differently to the flame and soda. The edge of a square pot can create a natural barrier to the flame, both accepting and deflecting it to create a protected area and point of contrast. The flame may also move over an edge, creating a much different mark than that of a round form.
Plates sit flat on the shelf and are often bypassed by direct flame. Stacking plates on wads or shells may create higher flame velocity between them, which can result in interesting marks such as dots or flame trails. The height at which a shelf sits above a plate also plays a role in the velocity of flame reaching that plate as well as the amount of soda affecting its surface. In an effort to create a form with the ample flat surface area of a plate but capture more of the flame directly, I began to construct envelope vases, which are essentially two plates, stacked on end and attached on three sides. These particular vases record the path of the flame on two different sides that are typically contrasting because the flame is not able to wrap around the piece.
Planning and Placement
The placement of each piece in the kiln has a dramatic impact on the overall surface. Prior to making a body of work, I’ll draw each piece that will be in the firing. Forms will also be drawn next to one another as well as all of the possible configurations of pots on each shelf. The idea is to anticipate the marks that will be left on each piece and how the flame will be directed through the kiln. Proximity of pieces to one another, to the shelves, and to the walls will have an impact on their surfaces. A pot that is close to (or touching) a shelf, wall, or other pot will have a more pronounced and protected mark. The further pieces are spaced out, the softer and more subtle the variation of color and marks will become. The difference in results caused by leaving between 1 and 4 mm of space between pieces may be substantial.
Placing two round pots next to each other on a kiln shelf will create a much different flame path (and different mark) than placing two angular pots near each other; the same goes for pairing a round and angular pot. Two envelope vases placed next to each other face to face will create a highly protected area between them. Wads or shells can also be placed between pots to create marks and points of flame constriction. I use a wadding recipe that is meant to be porous and create darker marks on the piece. The shape of the wad also plays a role. Think about round and angular wads and what marks they might leave.
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.
11, 12 Pots are pre-wadded and then covered with plastic to keep the wads from drying out before placing the pieces on a shelf.
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.
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.
15–19 The back stack is loaded first. Pots are positioned to create good airflow and an opportunity for the soda and flame to reach each piece. Iron-rich wads are also placed in between pieces in anticipation of the path of the flame in order to create particular protected marks. 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.
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.