Smoke Fired Ceramics

Smoke Fired Ceramics

Raku is a popular ceramic process whereby the red hot ceramic object is withdrawn from the hot kiln and exposed to organic materials. It blackens the clay body surface and contributes interesting surface colors to the pot, particularly if the  potter adds creative chemicals or organic materials in the process.  One other way to get a smokey surface, typical of pit fired native firing, is "smoke firing" the pot.  I would call Smoke firing a sub-process of Raku, but it is really different in a number of ways. 

Smoke firing is generally practiced on bisqued clay pieces, meaning the pot is fired to a low temperature to make it stronger and more resilient to the smoke firing process.  The low fired pot is then put in some kind of container filled with organic materials and ignited.  Often this "smoke fire kiln" is little more than a metal barrel with some sort of lid (to keep in the smoke).  The combustionable material can be leaves, shreaded paper, firewood, or whatever is on hand.  While Raku firing is generally in the range of cone 08, I am guessing the smoke fire environment is cooler than cone 010.  

The smoke fire process relies on the characteristic of the earthenware fired pot to absorb smoke from the heavily reduced kiln environment.  The areas of the kiln that have oxygen will fire cleaner than the areas where the smoke builds up, creating interesting responses to the process.  I have seen black ware from the Southwest called "Oaxian ware" or other local names.  If the smoke fire piece is refired in an electric kiln the smoke will be burned off and the effect removed.  Smoke fire pieces are almost entirely decorative and they don't make good kitchen ware pieces. 

Let's review a smoke firing

We will load two barrels, like those above, with shreaded paper,  stack some pots in the material, ignite the material, and then let it slowly die out from lack of fuel.  Then, we let the pieces cool for a while, remove and wash them, and perhaps treat the surface with some additional surface coatnig.   Here is a closer look at the loaded barrel. 

and a closer look at the shreaded paper

The pots are both filed with shreaded paper and buried in the shreaded paper.  The barrels serve as a saggar.  In fact, in some cases, potters have filled a saggar with leaves and a pot, and inserted it into a kiln to be fired normally.  When the combustionable materils is ignited by the temperature of the hot kiln, it slowly burns and creates the same smoke fired effect we will get from the smoke fired barrel.  

However, the reverse of this may also happen.  That is, the saggar is used to keep the pot clean and away from firing materials, particularly in a wood fire pit kiln where the potter wants a clean surface.  We can be relatively certain that Casas Grandes pottery was fired in a pit kiln with firewood (1200AD to 1450AD).  However, the only way the Casas Grandes pots could retain their clean surface designs would be for them to be isolated form the reduction of  the firing process.  Some CG pottery has smoke clouds, but the potters seem to have only accepted occasional occurances of smoke firing and probably isolated the pot surfaces from the firing in some manner.  I do not have evidence that the CG potters used clay saggars or even that archaeologists have found any saggars at CG.

Smoke firing can be enhanced with the aid of creative saggars also.  Some modern potters use aluminum foil to wrap the pots or portions of the pot to isolate smoke firing from  the surface.  And, in some cases, potters will wrap organic materials or chemicals next to the pot surface and hold it there with aluminum foil.  The relatively low smoke firing temperatures will not consume the aluminum foil.  I will conduct some experiments with Aluminum foil saggaring at the YVCC smoke firing, May 26. You are welcome to stop by and see the process.  Here is smoke firing in progress.

The barrels have just be ignited and covered.  I stop up holes in the lid with wet clay.  You can see small vent holes at the bottoms of the barrels.  Without the breathing holes there would not be enough oxygen for combustion and the paper would be extinguished. 

Regular iron barrels will last a number of firings.  YVCC always calls both Clean air Yakima to make sure it is an approved "Burn day" and also the city fire department so they know where the smoke is coming from.  Actually, if the firing goes correctly, little smoke escapes the ceramics yard. 

Here (above) the firing has been burning 3 hours and is almost completed.  Because the firing barrel is messy, I let it burn out and cool for a day or two before popping it open.  Then I remove the posts, wash them, and let them dry where they won't freeze.  Once they are completely dry, they will withstand freezing temperatures.  Here is another smoke fired jar.  You can see that the black pattern is not uniform. Subtle colors are and hues often result from smoke firing, 

and here is a more successful example (below)  that is now at Oak Hollow Gallery.  Personally I like the blacker jars.  Contrast can be enhanced by smoke firing burnished jars with white slip covering.  I often wax the jars at the end of the process to bring out the colors.  Sometimes I put a protective earthenware glaze (cone 06) inside the pot before smoke firing.  Technically one could make pickles or beer in one of these jars with the interior glaze but I never have?  Flip back in this blog to "Ceramic Jars" for more on this particular (unique, native) clay form.  

I hope to smoke fire a couple of my (fake) Casas Grandes copy jars.  They are smaller than the jars in this post.  I also hope to experiment with aluminum foil saggars on May 26.  I will have a set of Nuevo Casas Grandes" jars at the Oak Hollow show after June 7.  Stop by the show opening and chat.