Raku Firing Techniques | Glazes
Many people are interested in Raku firing. In this tip we've got an overview for beginners, as well as some tips from an expert (for those who already know the basic technique).
Raku is an exciting ceramics firing technique because you are so involved in the firing process. You've got glowing-hot pots, smoke, flame, and nearly immediate results (compared to a typical 10 hour kiln firing cycle)
The results are also very unique from other firing processes. Many people are attracted to Raku because of the bright metallic colors you can get from firing copper glazes, while some people prefer the crackling effects you can get with either slips or glazes. You also get deep contrasting carbon colored effects, which compliment the metallics and cracking.. Because Raku is a low fire technique, the resulting pots are not especially durable, but they are all unique and very interesting to look at.
Olympic 28" raku kiln
In raku, a bisque-fired pot is brought up to temperature in a fairly regular looking kiln, with one exception. A raku kiln allows easy access to the wares inside the kiln while they are still at high temperature. A good example is the Olympic raku kiln (shown to the right). On this kiln, an over- head lift mechanism raises the body of the kiln to allow access. Also, unlike other kiln firing, raku pots are not allowed to cool in the kiln. Instead they are removed with tongs while they are still hot.
The Bracker portable raku kiln
Moving quickly, the hot pieces are put into a reduction environment. A reduction environment is an enclosed space with a reduced amount of oxygen. Usually this consists of a metal garbage can with combustible materials inside, such as newspapers, saw dust, leaves, or pine needles. The piece is inserted into the garbage can, and the lid put on. As the heat from the pot burns up the combustibles, the oxygen inside the garbage can is consumed. After about 20 minutes, you can remove your piece/pot. And after some cleanup, you have a truly unique piece of art.
In a little more detail...
First you must bisque fire your pots as usual. Make sure you use a clay that is designed for Raku firing. It will be an open body with good thermal shock characteristics.
Next you can apply slip, apply glaze, or just leave the pot bare. The surfaces of the pot that are not covered with glaze will turn black from carbon from the post-firing reduction process.
The pots are placed in the kiln and brought up to the point of glaze melt. Although a pyrometer is sometimes used to monitor how fast the temperature is rising, Raku artists usually watch the glaze to see when it is ready to be reduced. Depending on the glazes and technique used, that might be when gets shiny, or when it bubbles and/or looks like orange peel. (The firing range is anywhere from about 1400 degrees to 1832 degrees F.) Sometimes Raku artists don't use glaze and then a pyrometer is used to determine when to pull the pieces from the kiln.
While the pot is heating up, you prepare your reduction chamber (garbage can) by adding the combustibles. There are many things you can use, but newspaper seems to work well and is abundant.
Wearing protective gear (gloves, face shield, etc.) you grab the hot piece from the kiln with your tongs. Then you place the piece in the reduction chamber (garbage can), and then you put the lid on the can. Leave it in there for about 20 minutes. (Note: If you want a more crackle in the glaze, on the way to the reducing chamber, spritz the pot with water from a spray bottle)
While you wait for your pieces to reduce, you can load new pots into your raku kiln (to keep your equipment efficiently used). In about the time it takes you to remove your pots from the reduction chamber and prepare it for the next usage, your pots will be hot in the raku kiln. Once the raku kiln is up to temperature, new batches go relatively quickly, about 30 minutes a batch.
After your reduced pot has completely cooled , Ajax cleanser is often used to clean carbon off the raku glaze and "shine it up".
After watching an instructional video, you could do Raku firing by yourself. But it is always a good idea to get someone experienced to help you out the first couple times.
More about raku kilns...
Olympic electric raku kiln
For firing a raku kiln, propane is often used because it is portable and has good heat-creating potential in a relatively small container. It has long been believed that you cannot use an electric kiln for Raku firings, (because the temperature shock from opening the kiln often would cause the elements to wear out quickly). This has not proven to be the case, and many people do use an electric kiln for their Raku firings.
Paragon Home Artist kiln can be used for Raku
If you go electric with your raku kiln, it's a good idea to have a power-cutoff switch installed on your kiln. This cuts the power to the elements when the lid is opened, to reduce the risk of electrical shock (should you make contact with the electrical elements with your tongs). The Paragon Home Artist kiln (left) can be used for raku firing and can be ordered with the cutoff switch
Still, it would be safe to say that the majority of Raku firing is done with gas kilns and propane tanks. This is at least partially because propane is portable, and Raku firing does generate smoke and needs a bit of space to be done safely.
WE GOT THESE ADDITIONAL TIPS FROM AMBER AGUIRRE, A RAKU ARTIST/EXPERT IN HAWAII.
In order to get nice blacks, it's not the amount of newspaper that is important, it's the speed in which you get the piece into the reduction container and get the lid on. Again, be super organized and prepared. Always keep your lids in the same place each time, such as leaning against each garbage can..
Keep the lid on the can, even after you have removed your piece at the end or reduction, or the combustibles can flame up
If working alone, 4 or 5 pots is about the most you can put in the kiln at a time and still be able to get them into individual reduction chambers, and get good raku firing results (before they cool too much)
Propane tanks can "freeze up" and restrict/stop gas flow. As a result, you can no longer generate the heat you need to fire the kiln. This happens because the liquid propane in the tank requires heat to turns into vapor. So much so, that it will take the heat from everything around it, mainly the tank and the gas expansion valve. If that happens too rapidly, it will freeze up the valve and limit the gas will flow. Therefore, if you are firing a lot of pieces, it helps to have multiple propane tanks and to switch between them after every firing
If you're having trouble getting your gas kiln to heat up, you probably aren't getting enough air/oxygen in your kiln. You need large holes especially near the burner and at the top of the kiln. This allows the gas/propane to burn efficiently.
If you are using newspaper as your combustible, and if it touches your pot, it will leave a mark (which you may or may not like on your pot). Amber doesn't fill the can with torn up newspaper like most people. She just puts 1 piece of newspaper at the bottom, and lines the sides with two more pieces of newspaper. Then she places the pot on the container bottom, so the newspaper doesn't touch the sides of the pot
EQUIPMENT AND TOOLS
Potentially any kiln could be used for Raku, as it's really the post-firing reduction that makes it happen. However, certain kilns are commonly used because of the access to the pot that they allow. Browse our selection of Raku kilns.
To see more about Raku...