Raku Firing

Kristie Chang

Professor Katz

Material Sciences


Raku Firing

Raku is a very complicated and fascinating version of firing ceramics. Simply put, it is the method of removing bisque-fired ceramics from a kiln without letting them cool down and then moving them into some type of closed container with some material within it that will create a flammable atmosphere. The results vary widely, and will change from a variety of factors. Some of them are the amount of time it takes to move the piece from the raku kiln to the enclosed container, how long the piece sits in the enclosed container, the thickness of the glaze that is put on the piece, and the type of raku kiln being used. The results are a lot less reliable than traditional kiln firing, which makes the pieces much more unique. The history of raku firing, the many nuances in the processes and results, and the uniqueness of these pots are all facets of what makes raku firing such an interesting method of creating.

The history of raku firing is very long, and instances of it can be seen in different parts of the world. It was originally invented in 16thcentury Japan, in a province called Kyoto. The original raku pottery pieces were used in tea ceremonies and were considered to be extremely valuable, and they had an immense amount of meaning behind them. These traditional pots were used as Ceremonial Tea Ware of the Zen Buddhist Masters, and the word Raku signified enjoyment of freedom. The raku tea ceremony bowls incorporated Zen principles such as harmony, reverence, purity, and tranquility and both the process and specific results in their tea bowls incorporated an avoidance of luxury and a natural aesthetic that was greatly valued at the time and in their culture. These specific bowls were hand built, and the results from this artistic and spiritual process fit in with the Zen philosophy of Buddhism that inspired the invention of this amazing process. (Lavey.) The fact that these bowls were valued for their imperfections and asymmetry rather than those aspects being flaws is something that can be greatly admired about both the Zen philosophies that inspired these pots and the 16thcentury artists who continue to give inspiration to modern potters.

“According to the Zen Masters, its elusive, subtle, yet vigorous beauty is Raku’s only worth. It is valued because it is believed that the Spirit of the Maker is embodied in the form and revealed at the foot, which is traditionally left naked (unglazed). It is believed that if we are alert to ourselves, in contemplating the Raku form, we will recognize in it our own Spirit and Meaning. (Lavey.)”

This is the very beautiful and culturally rich origin of raku firing, and it has gone on to inspire ceramic artists all over the world for centuries to come. Artists often create to recognize their own personal meanings and embody some part of themselves into their preferred forms and methods of process, and around the world artists found different ways to preform raku firing and it reflected on their cultures just like it did from its origins. Raku firing can be a very personal and even spiritual experience, due to it being much more hands-on experience compared to other firing methods and the nature of the process and results.

The process of raku firing can vary from the traditional method of the pieces being removed from the kiln and then cooled at air temperature, to the most common contemporary method of removing the kiln before any cooling at all and moved into an airtight container with flammable material put inside of it beforehand which is commonly known as the more “Western” version. The flammable materials are most commonly sawdust or newspaper. This process starves the pot of oxygen, and the glazes react to this in very beautiful ways. The pots themselves are most often made from a stoneware clay, which tends to be a lighter color both in unfired and fired forms. The unglazed portions of the pots turn black through this firing process, due to the pot being starved from oxygen in this Western version where they are put into the airtight container. The container often is a metal trash can, but anything that is airtight and can safely contain the flammable materials will give the desired result of a reduction chamber that deprives the pot of oxygen which greatly influences the result of the finish, no matter what the glaze is. The lid has to be put on the airtight container very quickly to assure that the oxygen reduction happens at an ideal rate, and the amount of time taken to move the pot to whatever container it reduces in will affect the finish greatly. After the pot has cooled down, it is often cleaned because whatever the combustible material inside the reduction chamber usually leaves soot over the piece.

Due to this reduction process being somewhat aggressive and exposes the pieces to a great amount of shock, there is a relatively high rate of cracking or exploding. Another factor that can add to the higher likelihood of damage is the fact that the pot is moved during the firing, and has to be moved very quickly. In traditional firing methods, this is not an element that has to be considered since the pots sit in one place throughout the entire firing process.

Raku is a comparatively low-fire method compared to other traditional methods such as high-fire oxidation or reduction firings. Western raku is typically heated to around 1,650 degrees Fahrenheit which falls into the category of cone 06 which is considered low-fire. High-fire can go up to 2400 degrees Fahrenheit. Another difference is that traditional firing cycles can take up to 10 hours, with additional time added for the time it takes for the kiln to heat up and cool down enough to be able to take the ceramics out of the kiln safely. The pots must be taken out using tongs, gloves, and sometimes even a full protective outfit due to the risks of being burned. With raku firing, the firing cycle is very short: around 15 minutes to 1 hour in the kiln which is very unique for kiln firings.

The time spent after taking raku fired pots out of the kiln depends on whether it is done with the Eastern method or the Western method. The Eastern method often incorporates rapid cooling of the newly removed and still red-hot fired pieces in normal air temperatures or dipped or sprayed with water. The Western method is the one previously described where the pieces go through a post-firing reduction by being places in an enclosed container and starved of oxygen. (D’Souza.)

Another aspect of the raku process is that the kiln is heated much more quickly compared to other kiln firings, and this shock of heat combined with the shock of air temperature result in the unique appearance of raku pots having a heavily crazed or glossy surface. Whether or not the firing is done in the method where it is placed in the airtight enclosed container after being removed from the raku kiln, this shock of being taken out of the kiln still affects the pot. This process creates for a very unpredictable outcome which is one of the aspects that makes it so appealing to many potters.

Some of the more common contemporary raku finishes are a matte multi-colored finish, a high shine muti-colored finish, a white crackle finish, or the very interesting method of burned hair or feather finishes. Most glazes are suitable for raku firings, but there are specific glazes made for raku firings that take into account all of the different variables of the firing so they can produce more ideal results. Raku pots are usually not food safe, due to the risk of flaking on the pots and the nature of the resulting glaze finishes and they are also less durable than traditionally fired stoneware pieces due to being in the kiln for a dramatically shorter time period. Pots also have a more lightweight feel after being raku fired.

An interesting aspect that happens often with the multi-colored high shine and slightly metallic finish that is common in raku glazes is that after time passes, the color dulls due to oxidation. With the horsehair or feather method, the pot is taken out of the kiln and rather than being reduced in an airtight chamber such as in the Western method, it is left to be shocked by the air temperature and not reduced at all. These pots have no glaze on them at all, they are left bare and then burned with the horsehair or feathers while they are still hot. This process is very hands-on and produces some very interesting and beautiful results.

Raku firing is a very amazing process with a lot of science and history behind it. The history, process, and uniqueness of these pots are some of the many reasons that this method of firing is so prominent in the field of pottery. Learning about the rich history contributes to being able to participate in this process with added context and a wider outlook.

Sources Cited

Lavey, David. “Raku Process.” Raku History , Lavey Pottery Studio, www.newton.k12.in.us/art/3d/images/rakuhistory.pdf.

D’Souza, Sara. “Learn Everything You Need to Know About Raku Firing.” The Spruce Crafts , The Spruce Crafts, 24 Nov. 2019, www.thesprucecrafts.com/raku-firing-and-how-its-done-4059293.