by Edward Dix
At a seminar I attended in 1996, I learned that although the jô is a perfect cylinder, its surfaces are not created equal. A few weeks later this lesson was repeated with another familiar wooden “war club,” but with a twist — a 90° twist, in fact.
A diagram will help to clarify some cardinal points:
The “grain” of wood is the long axis of the thin fibers that make up the wood. In a jô the grain runs down the long axis, end-to-end. When viewing the end of the jô, your line of sight is parallel to the grain. The growth rings are laid down each year by layers of cells growing quickly larger in the spring season but more slowly as summer progresses, finally stopping in autumn. The growth rings appear as irregular light and dark bands. In white oak they are relatively thin and faint, but in other types of wood they are more pronounced.
Wood rays run perpendicular to the growth rings. They are bright and obvious in white oak, but are not easily seen in some other woods, like hickory or ash. These are also made up of lines of cells that in the living tree pass water, sugars and other bio-chemicals from inner layers out toward the bark and vice-versa.
When you strike with the jô, the line of force is perpendicular to the grain but could be at any angle to the growth rings. As I understood the lesson at the seminar, strikes should be made with the radial face because the jô is stronger in this orientation than when force is applied to the tangential face. The line of force is kept perpendicular to the growth rings, as well as perpendicular to the grain.
I was a bit perplexed a few weeks later, when I picked up a Louisville Slugger™ (the finest baseball bats made) and hefted it as I’d been taught since Little League, with the trademark face up. Held this way, the bat would strike the ball on the tangential face of the wood. Here was a contradiction of what I’d just learned about striking with a jô. Had I misunderstood the instructions?
The next morning at the Bureau of Forestry library, I consulted a pamphlet produced by Hillerich & Bradsby Co., manufacturers of the Louisville Slugger™ bats. These bats are made of high quality, straight grained, white ash. The trademark is placed on the “flat of the grain” (i.e., the radial face), because the experience of many thousands of baseball players has shown that the bat is less likely to split or chip if the ball is struck with the tangential face.
I found the resolution to the apparent contradiction in the Wood Handbook: Wood as an Engineering Material, published by the Forest Service of the U.S. Department of Agriculture. Woods do differ in their response to stress loads placed on the radial face verses the tangential face. While in some species there is no difference in the strength properties of one orientation over the other, some exhibit greater toughness in the radial orientation than in the tangential, and about an equal number of species show just the opposite.
Small, (2 cm. square x 28 cm. long) clear, straight grained specimens of North American white oak, tested on a diabolical torture device by the Forest Products Laboratory, show 30–60 inch-pounds greater toughness when the load is applied to the radial face than when applied to the tangential face. Experienced students of the jô evidently discovered that there is a practical difference in Asian white oak as well.
Look at the end of your jô. If it’s made of white oak, the brighter wood rays will be easier to see than the growth rings. The wood rays will be pointing to the radial faces. You’ll quickly learn to distinguish the difference in surface markings on the different faces. Since the best bokken are also made of this white oak, it follows that a bokken manufactured with the radial faces at mune and ha will be somewhat stronger in striking. However, in the course of practice, a bokken takes many strikes on the shinogi, so there is probably little advantage to insisting on a particular orientation.
Ed Dix is a licensed instructor of
kenjutsu, holds black-belt rank in aikijutsu, and instructs the “practical jûjutsu”
class at the Itten Dôjô. Mr. Dix received a Masters Degree in botany from the
Pennsylvania State University and is Coordinator of Conservation Education
Programs for the Commonwealth of Pennsylvania Bureau of Forestry. He can be
contacted via e-mail addressed to edix@state.pa.us.