Offerings

Soda firing with natural gas is similar to firing a reduction kiln, with a few marked differences.

1. I spray soda ash (sodium carbonate) into the kiln at cone 10 temperatures. This coats the kiln and the pottery with a layer of glass that alters the surface texture and color of everything according to the path of the flame. The soda ash interacts with the silica and alumina in the clay and as well as the glazes as I spray.

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2. Loading the kiln is a fun and interesting process. Those of you who have loaded any glaze kiln know how pots are placed on shelves that are built according to the necessary height. In a soda kiln every pot, shelf, and post must be 'wadded' so that nothing fuses together. This means you can come up with interesting ways to place pottery in the kiln, such as firing a bowl upside down, or placing cups on top of a plate. You can fire bottles on their side, or planters rim to rim. The path of the flame

around the wadding makes for very beautiful flash marks that can be a big part of what makes the work unique from other firings. Now that you know a little more about the process, I will outline specific materials, clays, glazes, and slips that will be useful to use. As I said before, a big part of soda firing is how you wad your work and place it in the kiln, so being there during the loading process and experimenting with different methods of wadding can be fascinating. Wadding on specific clays, slips, or using particular materials can change the color and surface of your work dramatically. (note that I cannot wad any part of the pot that does have glaze on it, only areas with raw clay or slip)

In atmospheric kilns, it is important to use specific slips or clay bodies that work well.

There are slips that we will apply on bisqueware that I will make available. Copper, iron,

and rutile oxide stains can also have nice effects in the soda kiln when applied to raw

clay or bisqueware. Avoid mason stains/slips or commercial underglazes as the

reduction atmosphere as well as the soda does not lend well to their brilliancy.

 

Clay Bodies: recommendations

Continental Clay is the primary brand I use mostly due to proximity and quality.

1. B-Clay and B-clay with grog cone 5-10

This clay is a white porcelain-like body that is easy to work with and holds up

better than most porcelains in the soda kiln. Because it is not a true porcelain it

has enough impurities in it to yield a myriad of oranges and grays in the kiln. It is

a nice clay body to use on its own in the soda kiln, and will keep transparent

glazes brilliant.

2. Buff stoneware cone 5-10

This clay body yields a dark brown to gray in the soda kiln and is coarse in

nature. It is a nice clay body if you are looking for a more organic and natural

look.

3. Buff stoneware with Ochre cone 5-10

This is a very dark clay body due to the high iron content in the clay. It can yield

green, dark brown, and gray tones. It is similar to buff stoneware in texture. This

clay would look nice with porcelain slip applied over it in various ways to contrast

the dark clay underneath.

4. Soda clay cone 10

This clay body yields oranges. Unfortunately I have not tested this clay in the

soda kiln, but it is formulated to be fired in them so it would be a solid choice for

that reason.

5. Wood Fired Porcelain cone 8-12

This is the only porcelain clay body I would put in the soda kiln and expect colors

to flash with the soda. Typically most porcelains come out of the soda firing

with a coating of white soda ash on them, without flashing. I have not tested

this clay in the soda kiln, but I am confident it will do well because of its specific

formulation.

I personally recommend trying a variety of clay bodies to get an understanding of soda

firing. Most of the clays above can be fired to lower temperatures in an electric kiln,

(with the exception of the soda clay and wood fired porcelain), so if you have extra

pottery that you want to save for another firing style it is not unreasonable to buy various

clays at once.

I also am a proponent of wedging materials into your clay to make the final product

more unique.

 

Good additions to consider are flashing agents such as Gauge Red or Newman Red

Clay. (Note that these clays are stable at cone 10, DO NOT add low temperature clays

such as Red Art to your clay). I have found that the clay body can tolerate 1⁄4 cup per 1

lb of wet clay before it becomes difficult to throw immediately after, although if you let

the clay sit for several days this may improve.

Another addition is PURE silica sand. This addition will yield pearly white speckles

throughout your clay that can interact with the soda in various ways. 40 mesh silica

sand is best, but 75 mesh will be effective as well. 1⁄8 cups per 1 lb of wet clay will

produce interesting results.

Please do not use any form of ‘speckled’ clay or mid range clay bodies. We fire to

cone 10, and they will melt in the kiln.

Form recommendations:

There are various forms and styles that lend themselves to the soda kiln more than

others. If you enjoy making minimalistic, flat forms, loading these pots can be more

difficult, and are loaded similar to how they are in an electric or gas fired kiln. Wadding

them is more tedious, and firing these pieces on their side will cause them to warp

significantly. In addition, work that is thin has a tendency to warp a great deal more than

thicker pottery. The work is not sitting on a flat shelf, but wadding, and this causes it to

warp in accordingly. In general terms, anything that is thinner than 1⁄8 inch may warp in

the kiln. In addition, clay with grog (such as buff stoneware) tends to warp a great deal

less than clay without.

Bulbous, organic forms fire easily right side up or on their side, as their spherical nature

provides structure to the pot from any point. They will warp less when fired on their side,

or not at all. Avoid plates or wide based pots, unless you don’t mind them warping

slightly in the kiln. The soda clay and wood fired porcelain clay listed above may reduce

warping as well, because of their ability to withstand very high temperatures.

It is also extremely advantageous to make sets and stack your work rim to rim, foot to

foot, or one within another. Doing each of these will allow us to fit more work in the kiln

and create more flashing marks. Typically, cylinders with thicker rims (1⁄8 inch or more)

are easily stacked rim to rim (as long as the diameter of the rims are the same) or foot

to foot. Completely unglazed bowls can stack within one another to produce flashing

marks on the inside of the bowl. Utilizing this technique may be best for shallow, narrow

footed bowls. Closed forms like bud vases, jars, or teapots are also great to load

because they are less susceptible to stray wadding and can be fired in unusual

locations in the kiln.

Typically, loading an atmospheric kiln as tightly as possible will yield more dynamic

flashing results without using wadding props. I encourage people to make a wide range

of work that has varying sizes and shapes. Small pieces can fit into the empty spaces of

the kiln easily, and will change the end results significantly. Larger pieces can be

interesting because they capture a wider surface area from one side to another. With

that being said, work larger than 2 cubic feet or 30” in diameter/height will not be

guaranteed to fit in the kiln. Please bring 15-30 pieces to fire in the kiln. Not all your

work will be guaranteed to fit, but it is important that we fill the kiln tightly to yield

positive results.