Tag Archives: salt firing

Salt/ Soda Discussion Group

At NCECA I attended a discussion group that has carried on past Pittsburgh and is leading to some interesting post-conference disussions. At this year’s conference, the discussion group, Salt Firing Verses Soda Firing was led by Joyce Centofanti. One of the other attendees, David Hayashida, came up with the great idea creating an email list so we could continue our discussion and share recipes and techniques after we returned home. David put the list together and there was instantly a lot of information being passed around. Another participant, Pamela Theis, decided to take it one step further and create an Ning group (an social network site) that will allow us to continue to connect with each other, but to invite others out there who weren’t a part of the original group to add to the discussion.
So, if you’re interested in salt firing or soda firing, or even a hybrid, join the group and join in the conversation! It just began a couple of days ago, so we’re really just getting started.

Join the group Salt/Soda Firing 

I’ve been playing around on the site and found that you can upload photos and create this little slide show creator that you see below:

Find more photos like this on Salt/Soda Firing 

This is my page on the Salt/Soda Firing site, if you’re interested in seeing what you can do. I’m excited about the possibilities with this group. Soda firing is still relatively new so I think that a group like this that will allow us to share, trouble shoot and brainstorm can have a big impact. I hope you join us!

Artist Statement, April 2007

Looking back and moving forward.

Clay is one of the oldest materials used by humans, and its place in the lives of humans has changed and evolved as we have. It’s had a central place in a community as vessels that store water and grains. Today we most often see clay in the form of toilets, sinks, heater elements, and our molded dishes. With modern manufacturing we have personal spaces which we can easily fill to overflowing with things, so that few people can really say they lack any quantity of items. We store water in disposable plastic bottles, we store our food in layers of boxes and plastic bags, and once we’ve used these up we store the garbage in more layers of plastic until they can be taken away in the metal boxes on wheels. Things just flow through our hands, from factory to landfill, each item indisguishable from the next and inevitably forgotten once sealed in the earth.

So the place that clay has in our world today is much different than it’s been before. Clay is still plentiful, but it’s never been disposable. And clay as art still has the intention and purpose behind it that long ago would have been present in every vessel. It can be something to stop our busy lives for a few moments in the morning to meditate over our morning coffee out of our favorite mug. It can be a vase that with or without flowers, we can stop to think about how it is one of the few objects in our lives that are hand made and individual.

Each and every piece that I make is one of a kind. I often make pieces in a series, but because they are hand crafted and fired in a soda kiln no two pieces are identical. I’m drawn to the pieces with a depth that you can explore, with subtle nuances in the texture and patterns in the glaze. A piece where you can always look a little closer and see something new. You aren’t going to see that in a mass produced plate from Target, or a ceramic mug from Ikea. Our lives are busy and we often don’t allow ourselves to slow down and take a moment to reflect. I see clay/pottery/ceramics as a way to feel a connection with another person, and an excuse to slow down for a moment.

Clay is a material that has a long and rich tradition. I try to reference that history, but in the context of our contemporary world. This is why I love the process of soda firing, also a contemporary adaptation of an older process.

In the 14th century potters began using a technique called salt firing. By adding salt into a kiln, the pieces would be glazed without having to individually apply glaze to each piece. This was great for the very utilitarian pieces like sewer pipes and whiskey jugs. But by the 1970’s there were problems with the technique – black smoke comes from the chimneys, and it wasn’t very friendly to the environment or your neighbors. So another technique was developed, using soda ash and baking soda. The kiln is gas fired and this soda mixture is added to the kiln near the end of the firing (around 2200°F); the soda vaporizes and is carried on the flame throughout the kiln. The soda reacts with the pieces, changing their color and texture. The variations you see on the pieces come from the variations in the kiln – how close a piece is to the burner, how much room there is for the flame to flow across the piece, even the temperature outside or the humidity can effect the outcome. Even after firing soda kilns hundreds of times there are still surprises to be found in how the pieces react. The pieces that I have created for this exhibition are tributes to the unpredictable and unique effects of this process.

Emily Murphy

What is soda firing?

This post is part of a handout that I give to my soda firing students at Lillstreet Art Center. It is an attempt to explain a little bit about the history of soda firing, and tries to help answer the question, “what is soda firing?”. It is not the full story, but I hope that you find it helpful.

Soda firing is an atmospheric firing technique where “soda” is introduced into the kiln near top temperature (2350°, ∆10). The soda that we use is: sodium bi-carbonate, also know as baking soda (the Arm and Hammer™ kind), and sodium carbonate, which is also known as soda ash.

“Soda ash is the trade name for sodium carbonate, a chemical refined from the mineral trona or sodium-carbonate-bearing brines (both referred to as “natural soda ash”) or manufactured from one of several chemical processes (referred to as “synthetic soda ash”). It is an essential raw material in glass, chemicals, detergents, and other important industrial products.”
USGS

The soda vaporizes and is carried on the flame throughout the kiln. The soda vapors create a glaze when it lands on a piece (or a kiln post, or the wall of the kiln). Wherever the flame travels- so does the soda. When placing the pieces in the kiln during loading, you have to think carefully about when and where you want a piece to get lots of soda, or when and where you want a piece to be more protected. The kiln must be evenly loaded because the flame will travel on the path of least resistance (and therefore the soda will also be traveling on the path of least resistance). You also have to think about whether or not the piece is glazed. The soda is basically a glaze, and when two glazes mix, they can react chemically with one another and run down the side of the piece. It’s beautiful when you can control the run- but can be disastrous when it gets away from you!

What is the history of soda? Where did it come from?

The predecessor of the modern day soda firing, is salt firing. It is believed that salt firing began in Germany in the 13th century. As many things go, it was most likely come upon by accident. Perhaps some salt soaked wood (from pickling barrels?) was tossed into the kiln for the wood fuel. The salt vaporized and glazed the pieces inside the kiln. It was a great time saving measure. No need to glaze the pieces before they went into the kiln. Old German jugs were salt glazed, along with tankards and sewer pipes. The pieces that we think of as early American traditional ceramics from the southwest corner of the US were also salt glazed. Can you picture a big whiskey jug with cobalt blue decoration on it? Those were salt fired. The process that I’m talking about is wood firing with salt thrown in. The salt easily glosses up a piece and helps the wood ash flux out. Salt vaporizes at a fairly low temperature and can work its way into all sorts of nooks and crannies. In a salt firing, the salt vaporizes and the sodium chloride splits into sodium and chlorine gas. When the chlorine is exposed to moisture, it forms hydrochloric acid. The acid goes into the kiln atmosphere and is released from the chimney. The remaining sodium combines with alumina and silica in the clay to forming a glaze on the surface of the piece.

Although the previous paragraph doesn’t help sort out what soda firing is, it does give some important background information. Salt firing continued to be a technique used by potters up through the 1970’s (and is still is used as a firing method today). In the 70’s as people became more aware of the environment, they realized that the black smoke and hydrochloric acid wasn’t such a great idea. A couple of graduate students from Alfred University, NY studied sodium alternatives to salt firings, hoping to find something that was more environmentally friendly, and maybe even something that could happen in an urban environment.

The results were soda ash and baking soda. They produce carbon dioxide instead of hydrochloric acid. The soda doesn’t get into all the nooks and crannies like the salt does, but it does produce brighter and more vivid colors. Pots are usually glazed with an interior or “liner glaze” because the soda vapors won’t work their way into those hard to reach places. You can achieve a rich glossy surface that is heavy with soda, or a pebbled surface that is also referred to as an “orange peel” texture. This is often juxtaposed with a “drier” area of the clay that wasn’t hit directly with the soda. It’s all of these varied surfaces together that make up the rich look and feel of a soda fired pot. 30 years ago, when soda firing first began, most ceramicists were just trying to mimic the effects of salt firing. In the last 5 years that has changed. The true characteristics of soda firing are unique and are something to explore and achieve.

The soda vapors aren’t actually colored, but they are reacting with the alumina, silica and iron in the clay (and slips) to create the various colors of flashing, and associated textures. The resulting colors can be a range of oranges with yellow and red tones, to rich browns, golds and tans. If there is some copper in the kiln, there can be pink blushing. Or a cobalt glaze on a piece can cause a blue twinge to the soda. Sometimes the carbon from the firing can add a gray hue that can look like shark skin on porcelain.

So perhaps now you know a little bit more about soda firing.


I’ve included the recipe that I use for my soda firings below.

My soda recipe: (a variation on Gail Nichol’s process)
2 lbs. soda ash
3.5 lbs. sodium bi-carb
5.5 lbs. whiting (calcium carbonate)
Mixed with ½ of a 5 gal. bucket of wood chips, and water

*mix the dry stuff with the wood chips, and then add COLD water. Just enough so it sticks together. It should have a consistancy similar to oatmeal cookie dough or tunafish salad.

-Add soda into kiln when ∆9 is soft. Add 1 ½ angle irons full of soda mixture through each port. Wait 15 minutes between additions. Usually takes 3 turns to add in all of the soda.