Tip #82: Raku Firing
Many people are interested in Raku. 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).
Basics
Overview:
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)
A beautiful example of a Raku pot - Amber Aguirre |
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. 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 glaze and
"shine it up".
After watching an instructional
video, you could do Raku 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 and can be ordered with the cutoff switch
Still, it would
be safe to say that the majority of Raku is done with gas kilns and
propane tanks. This is at least partially because propane is portable, and Raku
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.
 | Speed is important to get good results, so stay organized. Always put your tongs,
gloves, and goggles in the same place every firing. This keeps you
from wasting time hunting around for them. |
| 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 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 |
Learn more about Amber and see her Raku
Pieces
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. We
have some here: Raku Kilns .
Also Books, Videos, and Tools .
And Raku Glazes
To see more about Raku...
Google Image search
Raku Videos on
YouTube Raku
on Wikipedia
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