GALLERY subdivisions

The Raku Process - As many of these pieces are raku-fired, I thought those of you who are interested might like to know what "Raku" is. Please forgive me if this is too long-winded. I wrote this for my students who actually do raku.

History:
The raku method originated in Japan in the 1400’s. The process arrived in the U.S. in the early 1960’s and was modified with the introduction of post-firing experimentation. This experimentation continues today and is the driving force of excitement for raku potters around the world.

Overview:
The bisque-fired clay ware is glazed and rapidly fired. The piece is then removed from the kiln while red-hot. The piece can be left to cool as it is, or it can be reduced for special effects by a post-firing treatment.

Reducing (the removal of oxygen):
The rapid cooling causes the melted glazes to quickly solidify creating a network of stress cracks. The red-hot clay piece is then buried in a combustible such as sawdust. The resulting smoldering fire turns the clay body black. The black clay body shows through the cracks and appears on the surface as a black crackle.
In the reduction process the metal oxides in the glazes lose their oxygen and become metallic and frequently iridescent. For example, copper oxide is green. When the oxygen molecules are removed it becomes copper metal which is a reddish color.

CuO (green) minus O (oxygen is consumed by fire) equals Cu (red copper)

Raku Clays:
Because of the extreme thermo-shock (the rapid heating and cooling), raku clay bodies should have some openness or porosity to allow the expansion and shrinkage movement. Therefore, most raku clay bodies have sand or grog in them. Clay, like porcelain, that has little or no grog frequently cracks during the process.
The reduction of the clay body turns it black. Dark clay bodies tend to be blackest. The type of clay body will affect the degree of crackle obtained in reduction.

Raku Glazes:
The raku method is a low-firing procedure. Thus, raku glazes are low-fire. There are many books and online sources for raku glaze recipes. The basic formula is a ratio of 80% gerstley borate and 20% feldspar. You can then add colorants to suit your tastes.
Our twenty-plus years of raku firings have produced some remarkable glazes. We have also had good results with commercial low-fire glazes which melt at cone 06 to 05.
Many factors affect the outcome of raku glazes. A few are: the application thickness of the glaze, temperature of firing, outside weather, type of clay body, reduction or not, type of material used for reduction, etc. This large number of variables causes a wide range of glaze results and control is mostly left for the gods to determine. I think the chance element is what makes raku firings so exciting… you are never sure what you are really going to get!

Loading the Kiln:
The glazed pieces should be preheated to avoid explosions from excess water absorbed during the glazing. Glazed pieces should not touch each other. Sufficient care should be taken to allow the movement of heat throughout the kiln (gas firing). Caution should be taken not to touch the shelves or posts with your hands as they will be very hot from previous firings. Wear gloves and no loose clothing.

Firing the Kiln:
After the ware has been carefully placed in the kiln and the lid or door closed, it is time to light the kiln. (I am referring to a gas kiln throughout this write-up.) It is best to have two people. Using a lighter (the long handled ones are best) one person will FIRST strike a flame and hold it at the end of the burner. THEN the second person slowly turns on the gas until the burner ignites. ALWAYS LIGHT THE FLAME BEFORE TURNING ON THE GAS TO AVOID THE KILN FILLING WITH GAS AND EXPLODING WHEN THE FLAME LIGHTS.
Start with a very low flame to help rid the ware of any remaining water (avoids pieces blowing up). Gradually bring up the heat. The average firing should only take ½ to ¾ hour. Look through the spy holes from a safe distance. Eye protection such as dark glasses should be worn. The glaze will first sinter, than bubbles appear like boiling, and finally the glaze will settle into a visible sheen. When all glazes have this sheen, shut off the gas.

Unloading and Reducing the Pieces:
Prior to unloading the kiln prepare several metal containers for reduction. Reduction containers (metal garbage cans work well) should be filled part way with a combustible material such as sawdust, wood shavings, dried manure, dry leaves, or shredded paper. A lid for each container should be kept close by.
Now, open the kiln door or remove the kiln lid. The pieces will be red hot. Using metal tongs carefully remove a piece from the kiln and place it into the reduction container. It will bust into flames, so be careful not to stick your face into the chamber.
Cover the piece with more sawdust (or what ever you are using for a combustible). The flame will quickly die from lack of oxygen. Put a lid on it. What will happen is that since there is plenty of fuel (sawdust) and plenty of heat (from the pot) the desire to burn is so great that the third necessary element for fire… oxygen… will be grabbed from any source where it can be had… from the glazes and the clay body. See the paragraph on Reducing above.
After about ten minutes you can remove the pot from the reduction chamber. Be sure to use tongs or heat-resistant gloves to pull out the piece. Place it in a safe area to cool. A word of caution here. Most burns occur by people handling a piece that has been removed from the reduction chamber and is sitting out cooling. It looks finished so the tendency is to pick it up in your bare hands. Ouch!

Cleaning and Finishing:
As the piece emerges from the reduction chamber, it will most likely be coated with a sheen of carbon and soot. The ware will need to be scrubbed to reveal its true colors. A piece may be cleaned with water and an abrasive such as Ajax. A toothbrush will help get into hard to reach places. I have also had success by burning off the soot with a propane torch, but you have to be careful not to leave the flame in one spot too long or the piece will crack.
Because of the porous nature of raku-fired pieces and the crackle glazes, raku pieces are not good for holding liquids. They are a decorative art. People have tried to seal the surfaces with waxes and oils, but nothing is completely safe. A cutoff plastic shampoo bottle can be hidden in raku vases to hold water for flowers. Also, you can use a raku platter to serve crackers and cheese, but wash carefully. Don’t run raku pieces through the dishwasher.

Conclusion:
I have given you a brief rundown of the raku process. There are many variations to the process. You can find quite a few books and articles on the subject as it is very popular among contemporary potters and collectors alike. As you participate in the process, you will gain a great experience and appreciation of what it means to RAKU.
You may even become hooked.

-Palul