From offerings at Buddhist temples and Shinto shrines, to scenting of spaces for purification or personal enjoyment, to the noble and refined experience of the ritual appreciation of fragrant woods of Kodo, the practice of using ash and koro (incense burner) have a rich tradition in Japanese incense culture. Koro have been highly collected for not only their utility, but their beauty as works of fine art for centuries. Traditionally filled with ash, the koro/ash combination provides the perfect environment from which to enjoy Japanese incense as it was meant to be experienced, fully and completely. With a little knowledge and some simple preparation, using ash with a Japanese koro is easy to do and provides an optimal environment for the full appreciation of the rare and fragrant ingredients used in Japanese incense.
Traditionally the ash used in Japanese koro, be it for simple daily enjoyment or during the ritual appreciation of Kodo, is rice husk ash (RHA). Produced by incinerating rice husks, during the burning process the evaporable and organic components of the husk are burned away leaving primarily silicate residues, a basic chemical building block found in sand. A versatile byproduct of rice production, RHA is used extensively in the production of concrete and as a suspension agent for porcelain enamels. The ash has a rich tradition of being used in ceramic glazes in China and Japan, quickening the melting point of the glaze.
There are many benefits of ash for listening to incense. The ash provides an excellent thermal insulation material for suspending the incense within the koro. Ash is traditionally used in the Kodo ceremony to cover the burning charcoal used to heat a fragrant wood chip, providing a thermal barrier between the red-hot charcoal and both the koro and the listener. Fine grained and lightweight, RHA is also breathable, allowing the flow of oxygen to the burning incense while retaining the heat of the burning ember, allowing for the full combustion of the stick even below the surface of the ash. Finally, RHA is odorless and does not absorb odors, providing a perfect olfactorily neutral base that will not color the notes of the fine and rare fragrant ingredients in Japanese incense.
Burning of rice husks in open air will always produce silica ash, however the temperature of incineration is an important factor related to the color and quality silica ash produced. Up to 1100ºF the RHA produced is pink in color and will not substantially generate amorphous silica. Between 1100ºF and 1500ºF amorphous silica ash is formed and turns gray in color. At over 1800ºF the amorphous silica ash takes on a white appearance and is considered the most “pure.” All ash used with incense is at least gray, with “milky white” considered the purest and the most popular type of ash sold for incense use. The finer and whiter the ash, the higher quality and purity it represents.
To prepare the koro to receive incense is a simple process that requires little more than adding ash. Each koro will require a different amount of ash depending upon the size of the burner, but a good rule of thumb is to fill the koro to no more than 80% full or a depth of 1.5” to 2” of ash. Some koro will require more ash and others less depending upon their size and shape. When filling a koro with ash it is best to do so in an area that is easy to clean and away from breezes as the ash is very light and can spill about if care is not taken.
Once the ash has been added to the koro avoid the temptation to compress the ash flat. This is a common mistake. Often this is the leading cause of incense sticks not fully burning below the surface. Compressing the ash reduces the flow of oxygen and doesn’t allow the ash to breath. The ash press tool often seen used to prepare a koro for the Kodo ceremony is used to draw the ash over a piece of burning charcoal more so than to compress the ash. The flat ash presses seen in many YouTube videos used to create a pristine flat ash surface are not intended for stick incense, but to create as a base for lines of powdered incense to be burned upon the surface of the ash. Burning stick incense utilizes the ash as a simple support and requires the ash to remain uncompressed to allow oxygen pass through it to reach the portion of the stick below the surface of the ash. To somewhat flatten the surface, instead of compressing the ash down, gently tap the bottom and sides of the koro to allow it to settle naturally until the surface is uniform.
Finally, after the ash has been added and settled, remove any excess ash from the top and sides of the koro that may have spilled while being added. Traditionally this is done with a feather tool or feather brush, but a soft dry towel can also be used. Once this is complete, the koro is ready to be displayed and used to burn incense.
Burning incense using a koro with ash is a very easy process that requires little effort at all. By following some simple steps, not only will incense sticks burn completely and safely, but the the smoke rising from an elegant koro themed to the seasons or one’s decor will add to the experience of listening to the fragrance.
First, if the koro has a lid, remove it and place it safely beside the koro. The koro lid is intended to cover the ash between burning to keep the space clean and neat looking, emphasizing the beauty of the koro rather than the ash within it. Even should the stick be placed horizontally on the ash or another form of incense used in conjunction with ash that allows the lid to be replaced during burning, removing the lid during burning is still recommended for two reasons. First, burning incense with the lid on will restrict the flow of oxygen to the burning incense which could reduce the temperature of the burning ember. Reducing the burn temperature of incense could diminish or alter the fragrance released. Second, Japanese lidded koro are often collectable works of fine art. Replacing the lid during burning will expose the lid to high quantities of smoke very near the burning incense leading to staining and discoloration of the lid. It would be a shame to give a beautiful Japanese koro over to the soot gremlins!
Once the lid is removed, the ash should be stirred to add oxygen. However, this need not be done each and every time incense is burned in the koro. Over time the ash will settle and absorb moisture from the ambient humidity in the environment. In more humid months or in environments which are more naturally humid such as those with more temperate climates, stirring of the ash will be required more often. Traditionally, ash is stirred using metal “fire” chopsticks in a clockwise motion. However, any implement that allows the ash to be broken up and “fluffed” can be used. The goal of stirring the ash is to incorporate oxygen into the ash and break up any ash that has absorbed moisture. Stirring is easy, and only takes a minute to do, but it ensures that the entire incense stick below the surface of the ash will be consumed. As a rule of thumb, stir the ash until almost no resistance is felt and the ash is “soft” and “fluffy” looking.
Next its time to add incense! Light the incense stick and place it vertically in the center of the koro with the lit end up. The stick should go into the ash effortlessly. If the ash presents marked resistance, then it needs to be stirred. How deep to place the incense stick into the ash will depend upon the length of the incense stick with longer sticks requiring more depth of ash to support them. The goal is to place the stick far enough into the ash so that it is safely supported and will not move if the koro is brushed up against or if the stick encounters a breeze. Placing the stick vertically also ensures that the incense will burn at the optimum temperature and duration. Alternatively, the stick can be broken to fit the mouth of the koro and placed horizontally directly upon the ash. In this orientation the stick will burn more quickly however.
Finally, once the stick is consumed the lid of the koro can be replaced covering the ash within until the next use. The koro can continue to be displayed in this unused state, adding a refined elegance to any space.
Maintaining the ash in the koro is often a matter of personal preference. Some prefer to remove the incense ash from the surface with a sifter or spoon after every burning. This is not necessary however, and ash can be reused over and over for months with little attention beyond regular stirring. RHA by itself is odorless and will not absorb odors. However the same is not true of incense ash. As incense is repeatedly burned, incense ash will build up in the koro. This ash can easily be stirred into the RHA and mixed away. But over a long period of successive burns, this can lead to the faint odor of past incense also building up in the koro. As a general rule of thumb, for daily or mid-grade incense this is generally not a cause for concern. However, when listening to rare and expensive incense such as Kyara or fine Aloeswood incense, the odor of previous incense would be unwanted as it may color the purity of these rare and fragrant woods. For these types of applications some prefer to ensure the koro is filled with fresh ash or have a special koro reserved for only burning these types of premium incense.
After many successive uses over a period of months, the ash may become dirty and need to be renewed. There are two ways to do this. One is to remove the ash from the koro by sifting it through a common wire kitchen sifter on to tin foil, then baking the ash at 450ºF for approximately twenty minutes, allowing it to cool, then returning it to the koro. But with the economical nature of ash, its often easier to just replace it when it becomes dirty enough to consider renewal.
Ash often scares many new to Japanese incense away from using it with a koro. Without the proper knowledge it can seem a messy and difficult process that is just not worth the effort. But by using the simple steps above, the combination of ash and koro is easy to set up and even easier to use in the traditional way Japanese incense has been experienced for centuries. Once the koro is prepared with ash, it can be used quite easily and repeatedly for a significant length of time, and the fragrance of Japanese incense burning in an elegant koro will add greatly to the experience along the Fragrant Path.
As a final note, remember no matter how Japanese incense is enjoyed, it is indeed burning, and as such a fire hazard. Before burning incense, familiarize yourself with incense safety precautions, and never leave incense unattended or burn where children or pets could come in contact with it.
This page is part of Kikoh's Fragrant Path: An Introduction to Japanese Incense series. This series of posts is intended to help provide greater information and understanding as you progress along this fragrant path. Learn more...