The qualities that define the character of Bokken, Jo and other traditional Japanese wooden weapons, rest entirely on the integrity of the material itself. There are hundeds of wood choices overall and many regional varieties worthy of consideration but as we shall see in this section there are actually very few that are well suited for all situations that martial artists encounter in their weapons training.
The Japanese have always used their native evergreen white oak (Shiro Kashi) for most training weapons used in paired practice where there is likelyhood of impact with a partner's wooden weapons or armor. Kashi isn't generally considered a "fine" wood but its tough, reliable, relatively dense character is well suited for impact tool handles and martial art equipment. Many other materials and wood species are available in Japan. Unique weapons of unusual construction and materials, including several superb tropical varieties, are produced but only intended for settings appropriate to their scarcity, cost and appearance. Centuries of practical wisdom support this distinction between the utilitarian and the formal as it relates to martial art weapons.
The extension of the Japanese martial arts to other parts of the world, where no native tradition exists in the manufacture of related practice equipment, fosters attempts to produce traditional wooden swords and the like without the benefit of any accumulated local wisdom or reliable material from local sources. Because of this, there has been a tendency of non Japanese to overlook a distinction which is taken for granted in Japan - the role of materials suitable for routine practice and that of materials which are appropriate for presentation and ritual. Instead, many foreign practitioners view all equipment on a purely "qualitative level" and perceive the value of one's practice as being influenced by the degree of beauty and precision of the weapon - a notion generally discouraged by both Japanese and non Japanese masters and one, I think, that remains an obstacle in the development of weapons training. The following section is intended to guide the reader to an understanding of various materials and their appropriate use.
For both the utilitarian and refined, the wood is the weapon. Its strength, density, stability, color and texture are the potential for quality. Although a mediocre weapon may come from an exceptional piece of wood, it will always have within it the possibilities dictated by the the quality of the material. No amount of artistry will make a good practice weapon out of a mediocre piece of wood.
As it turns out, there are very few kinds of wood that are suitable for wooden weapons, especially ones longer than two feet or so where density and shock stength are important. Most hardwoods, especially the dozens of commercial species including native oak, maple, cherry, walnut etc. have mechanical drawbacks and most modern synthetic materials are not esthetically or historically appropriate to the traditional martial arts. It is little surprise that the materials chosen in this situation are not often seen in common woodworking where so many other readily available options exist.
The descriptions and information here include factual data concerning wood selections based on the production of thousands of wooden weapons for Japanese martial arts, published information and actual tests of hundreds of wood samples subjected to the stresses expected in paired practice.
It is necessary to categorize information and the following study, like all others, combines individuals of a species as if they were one but actually reflects an average of many unique members. In the case of natural wood there are significant differences within a species and the reader should consider the diversity: For example, American Black Walnut in general doesn't have suitable shock strength or dent resistance for this application and we would be tempted to unequevically extend this judgement to all Black Walnut. Under some (rare) conditions however, an individual tree may produce lumber that will produce a servicable and perhaps an excellent practice weapon. Several of the true hickories from a specific region (which will be discussed later) yield excellent quality lumber in general but an individual piece may be weaker than unusually good piece of material from an "inferior" species.
The history of the Japanese sword spans about a thousand years. Over that time, the essential features of Japanese blades are remarkably uniform but we see differences, mainly nuances, in their shape. Some are longer by a few inches, some shorter, some with more pronounced curvatures, some heavy and others light in weight. Many bokken reflect these differences but we also see wooden swords that are not direct imitations of live blades. In fact, Japanese wooden swords are not generally intended to mimic the shape, weight or feel of a live samurai sword but instead intended to develop specific skills and facilitate specific movements.