What is Soda Firing?
Soda firing is a method of atmospheric firing used in ceramics that involves introducing soda ash or baking soda into the kiln as it's approaching peak temperature. It is a process that welcomes an intense amount of variety in surface decoration, and has completely captured my interest and attention in the world of ceramic arts. I was very fortunate to have been taught by Casey Beck, an incredible ceramicist who specializes in soda firing and provided me with incredibly helpful insight and direction as I began exploring the practice on my own.
Below I wanted to provide a sort of resource hub for what I have learned, read, and experienced throughout my research and practice, in the hopes that other artists interested in soda firing might be able to gain some helpful information or ideas. I will continue updating this page as I come across more resources or information, and feel free to reach out to me as well if you have any questions or thoughts that you'd like to share!
Clay, Slip, & Wadding
The clays and flashing slips you use greatly influence the final result of your work. I have developed several different clay recipes that I like to use in my firings, as well as some flashing slips that give the surfaces decorative flashes that are more difficult to achieve with just a bare clay.
One notable aspect of the clays that are used in a soda kiln is the silica:alumina ratio, which determines how matte or glossy the resulting glazed surface will be. Gail Nichols and Casey Beck are amazing resources for further information about high alumina clay. The clay I primarily use sits right around the 3.5 mark.
Some form of wadding is always necessary when doing an atmospheric firing, so that pots don't get stuck to the kiln shelves by the soda that's traveling throughout the kiln. You can find various recipes out there - white wadding leaves a more white/bare marking, while red wadding can leave colors ranging from orange, red, or black. Some people also use seashells (stuffed with white wadding)
Access my clay and flashing slip recipes through my Glazy profile!
Kiln Loading
How the kiln is loaded is one of the most important parts of the process (in my opinion). The patterns created by flashing in a soda kiln are entirely dependent on where the pots are placed in relation to each other, and how the soda is allowed to flow between them. I would heavily encourage experimenting with this part of the process, as there is so much you can achieve depending on where and how pots are placed. I've even placed cups behind the bag wall, directly in the region where the soda is sprayed/thrown into the kiln.
If you're looking to achieve stronger flashing in your work it can be helpful to start out by using less soda, as this can encourage stronger flashing patterns.
Firing Process
For me, firing a soda kiln typically follows the same schedule as a regular gas kiln until it begins approaching the peak temperature. Usually firing to cone 9, once I see cone 8 starting to soften up and bend is when I begin adding soda to the kiln.
I usually add the soda in the form of a spray or in a dried paste mixture. For spray, I dissolve the soda ash in a garden sprayer with hot water, using around 1 gallon of water per pound of soda ash. I don't spray directly onto the pots, instead letting it pool and burn up on the sides. Also - be mindful of the tip of your sprayer, so that the plastic doesn't melt. For the dried paste, I usually combine equal parts soda ash and whiting, then mix them into a paste with water and divide into equal clumps that get wrapped in paper before being thrown into the kiln.
I opt for the spray method more often than not, and spray a bit of soda into each of the kiln's back ports for about 15 seconds each. Be careful of how long you spray, because in my experience spraying for a long time (30-45 seconds+) will coat entire surfaces with soda glaze and create very uninteresting and unvaried surfaces.
After I'm done spraying I usually let it soak for around an hour or so, allowing the kiln to build up enough temperature to fully drop cone 9.
Resource Library
Gail Nichols - Soda, Clay, and Fire
Casey Beck - CM Techno File Article
Stuart Gair - A Thoughtful Soda Approach
Harry Levenstein - Soda Firing Logs