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History of Raku
Raku is a Japanese word that can be translated as enjoyment, happiness, or comfort. In 1580, the potter Chijiro is thought to be the first to produce this form of ware. He developed a low-fire pottery process in which he placed ware directly into a red-hot kiln, then once the glazes had melted, removing the ware from the still red-hot kiln and allowing the pottery to cool outside the kiln.
This direct process was well received, especially by enthusiasts of the tea ceremony. In 1598 a gold seal was presented to Chijiro (or possibly his son) by the ruler Hideyoshi. This seal was engraved with the ideograph for raku. Raku thus became Chijiro's family title. The Raku family continues making their pottery in Chijiro's tradition; the current master is Raku Kichizaemon XV.
In 1940, British potter Bernard Leach published A Potter's Book in which he described his introduction to the process of raku. In 1948, American potter Hal Riegger began experimenting with the process and subsequently, beginning in 1958, to include it in classes and workshops he taught. Somewhere in that milieu of trial and experimentation, pieces began to be reduced in combustible material once removed from the kiln.
In 1960, American potter Paul Soldner also began experimenting with raku ware, moving it away from the traditional usage in the tea ceremony and developing a sense of playfulness as well as directness and immediacy that is inherent in the process.Continue to 2 of 12 below.
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Prepare to Fire Raku
Raku requires preparation before you take on this form of firing. First, you need to use a clay body that can withstand the thermal shocks it will go through. Second, you will need a kiln that is appropriate for the process. Third, you need to have the proper equipment.
Raku clay bodies tend to contain 30% to 50% non-plastic material, such as grog, sand, organic materials, or kyanite. Stoneware bodies do well in raku, with such additions.
Even though the clay body may mature at cone 5 to 10, for raku it should be bisqued, as usual, no higher than cone 04. This leaves the clay open and less likely to suffer damage during the extreme temperature changes.
Raku kilns should be small; they also must be easily opened, with the opening large and safe enough for the ware to be removed from the kiln while still incandescently hot. There is any number of styles that can be used for raku, but in my experience, a well-designed top-hat kiln works exceptionally well. Top-loading kilns should be avoided.Continue to 3 of 12 below.
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Open the Raku Kiln
Once the ware is loaded, the burner(s) are turned on. Since the kiln's interior size is so small, the internal temperature will increase very quickly into the incandescent ranges. Many raku firings take a half hour or less to get the kiln to temperature.
Watch is kept on the pots through one or more peepholes. Use UV-cutting safety goggles, since looking into hot kilns can damage the eye. Once the glaze can be seen to have become fluid and the surface has smoothed, the burner(s) shut off. Usually, this will be at about cone 08 (1735 F/945 C).
The kiln is opened immediately, while the interior is glowing incandescent. This level of heat requires safety issues be held firmly in mind as the kiln is opened and the work of quickly removing pots begins.Continue to 4 of 12 below.
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How to Remove Pottery from Raku Kiln
Removing pottery from the now-open raku kiln can take steady nerves, hands, and the right tools. It also must be done quickly, so not too much heat is lost before the ware is placed in the post-firing combustion chambers.
The Right Raku Equipment
Have and use proper gear while rakuing. There are hazards present from heat, smoke, and in the case of fuming with metal oxides, heavy metal poisoning.
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- Smoke inhalation is nothing to play around with. Use a dual-cartridge respirator with cartridges that filter out both particulates and fumes. If possible, a respirator that also has a faceplate, such as is used for welding. This will help keep smoke out of your eyes and protect you somewhat from the heat. Never wear paper dust masks. These can flare into flame right on your face.
- Hand protection is a must. Use heavy Kevlar gloves specifically made for high temperatures when handling glowing-hot pots. Leather gloves or gauntlets will not give you enough protection if you are handling hot pots directly.
You may want several sets of gloves for different operations through the raku process. Leather gloves and gauntlets are useful when working with the not-so-hot pots at the end of the smoking period, and are also good when using tongs.
- Raku tongs are another must. Do not use barbecue or fireplace tongs! They are not made to withstand the higher temperatures that you will be working with. In addition, they are often not long enough. As you can see in the photograph, this potter is using raku tongs to remove the glowing pots, one by one, from the kiln.
- Protect your arms and legs. Wear cotton pants and shirts. Jeans are a good choice since they are both cotton and a heavier weave. Never wear shorts, nylon or synthetic clothing or jackets.
Additional protection can be gained by adding more gear. Non-asbestos aprons, preferably that go down to the shin or ankle, are best. Raku aprons can be either made from Kevlar, Kevlar-like materials, or cowhide. Some potters wear full-hide welder's jackets.
- Do wear leather boots or sneakers. Never wear sandals, or nylon or synthetic shoes. Do keep all hair tied back, and do not let anything dangle from your clothing or head.
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How to Carry Hot Pots
There are several things to bear in mind when carrying hot raku pots away from the kiln to the combustion chamber. After having (and using) the correct equipment on hand, the next important aspect of carrying your glowing pots from the kiln is your "flight plan".
You should plan out and have a clear path to the combustion chamber you have previously set up. Plan ahead so you have minimal time with hot pots in the open air. This reduces the possibility of accidental injuries, as well as keeping the pots hot enough to ignite the combustibles in the chamber that awaits them. Here are some tips:
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- Keep the distance you need to move hot pots to a minimum.
- Clear away all debris and obstacles from the path. Avoid traveling over rough ground that could cause you to trip or stumble.
- If working with other people, make certain everyone knows the safety rules such as no running, no horseplay, and keeping out of the way of whoever is transporting a hot pot. Make sure everyone knows to let others know when they are transporting a hot pot.
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Begin to Smoke Hot Raku Pots
Smoking the hot raku pottery is an intrinsic part of raku for most potters. Before the pot is placed in the combustion chamber, the glaze must cool slightly so that the surface of the glaze won't be marred if that is desired by the potter.
Combustion Chambers: You will need a fireproof chamber for the combustion. Although the term "combustion chamber" may sound very scientific and aloof, what it really comes down to for many potters are upside down metal buckets that are either on a patch of dirt or within a metal pan, a metal trash can with lid or another metal container with a lid or that can be turned over.Continue to 7 of 12 below.
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Raku pottery is so hot when it comes out of the kiln that it causes paper to go up in a flash fire until choked off by the lack of oxygen. Combustion is necessary for the pieces to be smoked properly.
Combustible materials are usually fairly small pieces; this helps to ignite the largest amount of material possible. Another consideration is that material that is nestled against the pot's surface will leave the greatest smoking mark. Such materials include shredded paper, sawdust, straw, hay, dry leaves, seaweed, shredded cloth, nutshells, and so on.
Hot pots are placed in a chamber with combustible materials. A nest is created out of the combustible materials inside the bottom of the chamber. Extra material should be ready at hand to place inside and on top of the pot. Place the pot in the nest and pull the extra material around it.
The heat of the pot itself will set the combustible material alight. Once active flame has been established, the chamber is closed and the pot allowed to smoke for fifteen to thirty minutes, depending on the effects desired by the potter. Once the flame is well established, close the chamber.Continue to 8 of 12 below.
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Remove Raku Combustion Cover
Removing the cover or lid from the raku combustion chamber requires a continuing eye toward safety. Although there may be no flame apparent when you are ready to open the chamber, expect flames. The fire inside the chamber will often smother (causing copious smoke) but once the chamber is opened and oxygen is once again available, the combustible material will often burst back into flame, sometimes with an almost explosive rush.
Because of the smoke released when opening the chamber, be certain to use your respirator. Further, protective gloves are also needed to handle the now-hot metal of the combustion chamber as well as the pots themselves. The pots will no longer be so extremely hot, but may easily still be over 200 F. Handling pots at this stage can result in severe burns.Continue to 9 of 12 below.
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How to Clean Raku Pottery
Raku pottery comes out of the combustion chamber with ash and soot covering it. It must be cleaned before it can be handled with any confidence that your hands won't become immediately blackened.
Begin cleaning only after the pot is merely warm, not hot. Dunking still-hot pots into water can lead to cracking or breakage.
Use a dry cloth to wipe away the worst of the soot and unburned material that make be stuck on the pot. Then use a damp cloth to further clean away soot. For areas that are stubbornly dirty, I would suggest a small scrub brush in conjunction with a mild solution of dish detergent in water. This may also be helpful for cleaning the unglazed foot of the pot.Continue to 10 of 12 below.
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Typical Raku Glazes and Glaze Effects
Raku has some glaze effects that are somewhat typical. These include metallic glazes, luster glazes, and other glazes that are affected by the reduction atmosphere in the combustion chamber. Married with the smoked aspect of the ware, raku pottery is often easily distinguished from other types of pottery.Continue to 11 of 12 below.
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Breakage in Raku
Raku pots are a very fragile form of pottery and are easily broken. This can happen at any time during the process, sometimes no matter how much care is taken. Occasional breakage is a part of the process.
To help minimize the chance of breakage, take the following precautions:
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- All pottery should have very even walls, floors, and joints. Unevenness causes stress during heating and cooling which will be exacerbated by the extreme thermal changes the pot will endure during the raku process.
- Bisque pots before glazing and rakuing them. This reduces the chance of breakage due to the driving out of atmospheric and chemically combined water.
- Try to lift pots by capturing them around their body, as opposed to lifting them by their lips. If a pot is too wide to get the tongs around them, try and get a grip on their shoulder, further down from the more fragile rim.
- If the tongs are slipping on a hot pot, set it down immediately and get a better grip on it. Do not try to simply hurry up, since that often causes more jostling which in turn makes it more likely that the pot will slip out of the tongs' grasp.
- Do not grip too tightly with tongs. It is relatively easy to grip the pot so hard that the tongs themselves cause the pot to break.
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Raku and Functional Pottery
Plates such as the one pictured here are for decorative purposes only. Raku is decorative only due to:
- Softness of the clay body. The clay body is porous enough it cannot withstand continual heavy use without the risk of breakage.
- Softness of the glazes. Raku glazes tend to be very soft, which allows more permeability than other glazes. In addition, glazes crackle which means that substances (and bacteria) can become embedded in the cracks creating a health risk.
- Leaching. Raku glazes are often more susceptible to leaching than other types of glazes. Leaching is most likely to occur in the presence of an acid, such as orange juice.