Soda firing is an atmospheric firing technique where “soda” is introduced into the kiln near peak temperature, usually 2350°, âˆ†10. The "sodas" used are sodium bi-carbonate, also know as baking soda, and sodium carbonate, which is also known as soda ash.
Soda is commonly introduced by mixing it with water and spraying it into the kiln. It can also be mixed up as a paste and added to the kiln on an angle iron. Some woodfire potters will mix the soda with a small aount of water to form a paste, then lay the paste on a piece of wood to be stoked. The soda, once introduced to the heat of the kiln, will vaporize and bond with the surfaces of the pots to form sodium-silicate glaze
In the 1970's, several grad students at Alfred University started researching sodium alternatives to salt firing. With their investigations into soda bi-carbonate and sodium carbonate, soda firing was born. At the time, it was seen as something more environmentally friendly alternative to its predecesor, salt firing and as something that would be better to do in an urban firing. The environmental claims have been a point of controversy ever since. You can find more out about this controversy here.
The results can be quite different over the past decade or two, ceramic artists have really been exploring the surface that soda produces. The colors can be brighter than salt, and the surface can be "drier".
Methods of adding soda:
Gail Nichols "plaster" method:
HEALTH AND SAFETY PRECAUTIONS
Soda ash dust is an irritant to the nose, throat, and lungs. In combination with lime, it will form sodium hydroxide (caustic soda), which can cause alkaline burns. Wear impervious rubber gloves and a NIOSH (National Institutes for Occupational Safety and Health) approved respirator mask. Chemical safety goggles are recommended for eye protection, and long sleeves and trousers should be worn. These precautions apply to all preparation and handling stages for the calcium/sodium mix, including handling the firebox residue,
which is high in sodium hydroxide.
Light Soda Ash (Australian or calcined soda ash) 20 %
Sodium Bicarbonate (baking soda) 30%
Calcium Carbonate 50%
dd 9 U.S. fl. oz. of water per 1 lb. (600 ml of water per 1 kg) of dry mix.
Emily Murphy's woodchip method (variation on Gail Nichol's method):
Mixed together with 1/4 of a 5 gallon bucket of wood chips/ shavings.. Mix together well, then add enough *cold* water (while mixing) to the consistency of oatmeal cookie dough. Wear gloves and a mask while mixing. I add it on an piece of angle iron through the ports on the front of the kiln when c. 9 is soft. Add 1 angle iron full to each side. Temperature will drop with each addition. Wait for temperature to rise and surpass before adding next round of soda. Wear organic vapor mask while adding soda during firing.
1.75 lbs. of soda ash
2.25 lbs. of soda bicarb
4 lbs. of whiting
The soda solution is introduced into the kiln via a garden sprayer. I begin spraying the soda solution into the kiln as cone 8 is going down (approximately 2250° Fahrenheit). I slowly circle the kiln and give a few short sprays in each of eight ports—four in back, two in front, and one on each side. Then I let the kiln breathe and begin again. I am not interested in carbon trapping at that temperature with the soda. For my pots, I do not like the glossy graying surface that produces. So, I let the kiln breathe in between rounds. Depending on weather conditions, the spraying process usually takes about an hour. If I have not reached a soft cone 10 by then I will continue to fire in a neutral atmosphere until I do. If I find cone 10 getting soft before I have used my desired amount of soda, I will turn the burners down while I finish spraying the soda solution. In either case, I clear and lightly oxidize the kiln for 10–20 minutes before shutting down at cone 10. Whether bare clay, slips, or glazes, what I'm looking for is a soft and subtle, but clear and clean surface.
2lbs soda ash to one gallon of hot water
Soda Paste on Wood:
Flask by Matt Long
Low Fire Soda:
Cone 6 Soda:
Online Resources for Soda Firing:
Online articles about soda firing:
Salt and Soda-glazing article on Ceramics Today.
Soda Firing by Robyn Gough on Avicam.
A New Soda Kiln: a kiln conversion project by Robyn Gough, Maryke Henderson, Robyn Whitworth on Australian Ceramics.
Why Soda Glaze? by Maryke Henderson on Avicam.
Soda with Sparkle: A profile of soda glaze specialist Ruthanne Tudball by Judy Adams in Ceramics Monthly.
Painting with Fire by Gail Nichols on Ceramic Arts Daily.
In the Soda Zone by Mark Bollwinkel on Ceramic Arts Daily.
Soda Firing Resources: Books:
Soda, Clay and Fire - Gail Nichols
Salt Glazing, Phil Rogers
Soda Firing Glaze Recipes
Webpages with recipes for soda firing:
Bill Buckner: http://sodaglaze.com/glazebod.html
Julia Galloway: http://www.juliagalloway.com/alchemy.html
June Perry: http://www.shambhalapottery.com/technicallinks.html
Scott Cooper: http://www.negentropic.com/clay/process/glaze-recipes.shtml