The following is the first chapter of a book in process, titled
"Bokken, Jo, and Related Wooden Weapons." Other chapters cover the
design of various weapons used in Aikido training including
observations on wooden swords and their schools of origin.
Introduction
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.
Impact Strength
Whereas the quality of wood can be described from many perspectives,
one of the primary concerns here is its safety and strength during
contact which typically occurs with sudden impact. The following
chart, Impact Strength of Materials, shows the strength of various
materials when subjected to impact shock (with other wood) expected
during paired practice. The test uses a simple spring loaded ram* to
test samples of identical size. The sole purpose of the test is to
determine if a particular material has potential as a martial art
weapon but some wood species are included to provide comparative data
even if they would not qualify for other reasons.
(For those interested in the physics of the test: The strengh of
natural woods (used as structural members) is well documented in
published data where samples are subjecting to slowly applied
loads. This test however is specifically designed to test shock
strength as it relates to martial art practice. A hardwood ram,
attached to a fiberglass spring, impacts equal sized test samples on
the tangential surface. The spring's deformation is proportional
to the magnitude of the applied force. The impact energy is
calculated according to the relationship E=1/2ky2. Impact energy can
be represented as the square of the calibrated distance that the
spring is deformed. Samples are subjected to gradually increasing
impacts until failure. The numerical values on the chart represent
the impact energy that broke the sample. Most values are the average
of five or more samples of the same species. )
White pine is included for reference. American White and Red Oak, both
ring porous hardwoods, might have sufficient strength but their open
grain presents exposure to damage in those areas.
In many cases, very hard and heavy hardwoods such as African Ebony
prove to be relatively brittle. Other exotic species such as
Greenheart,Blackheart, Blackwood, Leadwood etc all tend to have
excellent resistance to denting but low shock strengh. These materials
would show little damage at lower impacts but might break unexpectedly
with a higher impact. Lignum Vitae, a wood with extraordinary
properties, invariably develops checking (either superficial or more
severe cracking) due to atmospheric humidity swings and its use a
martial art weapon would not prove to be a wise use of resources.
Click image for an enlarged view of the impact strength graph and included footnotes
or
click here for an Adobe Acrobat .pdf version.
Density
Along with impact strength, wood density is a key consderation in
weapon quality. It is usually measured as a ratio called specific
gravity. When wood floats in water, its specific gravity is less than
1 but there are a few varieties, mostly of tropical origin, that have
specific gravities greater than 1 and will sink. High density does not
necessarily translate into high impact strength. There are several
dense woods that have a much lower impact strength than other less
dense ones as shown below. Please review the information in the above
chart "Impact Strength of Materials" and included footnotes which
describe the impact test and clarify the data in the following
table.
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White Pine |
.35 |
86 |
African Ebony |
1.10 |
110 |
Red Oak |
.63 |
169 |
Purpleheart |
.79 |
173 |
Pau Ferro |
.73 |
173 |
Shiro Kashi (Japanese White Oak) |
.82 |
179 |
Honduras Rosewood |
1.00 |
189 |
White Ash |
.60 |
196 |
Birch |
.62 |
196 |
KWW Laminated Composite |
1.30 |
198 |
Coromondel Ebony |
1.10 |
202 |
Osage Orange |
.80 |
243 |
Impact Grade Hickory |
.775 |
345 |
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Although high density doesn't necessarily translate into high
impact strength, it has a major influence on performance and
maneuverability. It is almost always desirable for Baton (police
stick) , Yawara (¡short stick ~12"), Kobuton (hand weapon ~5"),
Tanto (wooden knife) and other short sticks under 24 inches. The
additional inertia is a major benefit in many defensive situations and
when the weapon is used for pressure point techniques, dense and
harder wood is much more efficient. For these applications, wood with
specific gravity over 1 is often best.
Bokken (wooden sword) and other longer weapons used in paired practice
should be chosen from a material with high impact strength. In some
cases, a wooden sword is intended to approach the actual weight of a
real sword and higher density materials (specific gravity greater than
1) are required but these weapons should not be used for routine
practice. Suitable higher density materials are almost always
costly. Most wood with high specific gravity is tropical in origin
(the laminated composite shown in the charts comes from reasonably
well managed domestic sources but is expensive nonetheless). The most
important consideration of all is the possibility of an impact which
exceeds the material's shock strength; a situation that becomes
more likely with a weapon over 24" in length and relatively slender
in diameter like Bokken and Jo. High density materials are harder,
with the appearance of being practically indestructable and sometimes
won't show damage prior to failure. An unexpected, complete break
may create a dangerous situation. The same precautions are advised for
very long weapons including Bo (long staff ~ 72") , Naginata
(Japanese halberd like weapon ~ 96"), Yari (spear up to 120"),
Juken (rifle/bayonet ~ 72") etc. if used in contact with other
practice weapons.
Materials
Different materials are appropriate for different weapons and
different situations. The following wood selections are described and
recommended according to their individual properties:
Shiro Kashi (Japanese White Oak)
Martial artists familiar with Japanese wooden weapons frequently refer
to this wood simply as "White Oak". It has a tight but coarse
grain structure and like North American White Oak, it has prominant
rays which give it a distinctive figured appearance. It's either
bone white or light tan in color and darkens over time. Shiro Kashi
differs in several respects from North American White Oak. While
related, the Japanese White Oak tree is evergreen and owing to its
continuous growing season, does not have a conspicuous open grain like
American White and Red Oak. Open grain structure, typical of the so
called "ring porous" hardwoods presents soft areas which are
more prone to impact damage. Kashi is uniformly hard, has excellent
dent resistance and has better impact strength than American
Oaks. There are two drawbacks relevant to its use in wooden weapons:
It is not stable; weapons of Shiro Kashi will frequently warp due to
changes in atmospheric humidity. Also, like other Oaks, it seems to
lose strength as it ages. In tests conducted on older samples from
wood that had been very strong, the aged material had lost its
integrity substantially. The older wood will appear dry and develop
cracks usually beginning with a grain separation in areas of repeated
impact - a sure sign that the weapon is weakening. Clearly, Shiro
Kashi should be considered a good quality utility wood, excellent for
several years practice but probably having a limited life span.
White Ash
The most well known and useful of the Ash family is White Ash. The
wood is strong in comparison to its weight and is often used for
baseball bats, tool handles, oars and paddles. Ash is noted for its
stability. It is less subject to twist, warp and dimensional change
than most North American hardwoods.
Ash is a ring porous hardwood with strongly contrasting spring and
summer wood. This characteristic results in alternate, relatively hard
sections with softer areas of open grain. Because of this, Ash is more
prone to objectionable denting when impacted on its softer areas and
is not ideally suited for weapons taking direct impact. Because of its
otherwise excellent mechanical properties however, and its tendency to
get smoother and improve with continuous handling, it is one of the
very best materials for long shaft sections on Yari and Naginata.
Birch
Birch is moderately heavy and hard with good strength. Its appearance
is very similar to Maple with an even, fine texture and tight grain
structure. White Birch refers to the white sapwood of the species and
Red Birch refers to the heartwood of the same tree. Birch grows
throughout the hardwood forests of temperate latitudes and is an
important commercial hardwood. Its high shock strengh and availabiliy
in thick, long pieces, making it a good contender for wooden Bo
staff. Naginata, Yari and Juken. In its natural state, its drawback is
its tendency to show impact dents where contact is heavy.
Birch is well suited to the production of veneers, In the 1950s, the
US Forest Products laboratory developed a process of drawing resin and
dyes through veneer stock and laminating the wood layers under
extremely high pressure to produce an enhanced composite product. This
material is generically known as Compreg (compressed, impregnated
wood). The variation referred to in this publication is the
"Laminated Rosewood Composite" of Kingfisher WoodWorks.
Impact Grade Hickory :
There are at least 16 species of Hickory native to Asia, Central
America and North America. Mixed hickories, appropriate for furniture
and cabinet work, are obtainable in lumberyards throughout the United
States. Varieties from New England, the Midwest, Great Lakes and
Southwest, including the closely related Pecan Wood, produce lumber
comparable in quality to many other North American hardwoods as shown
in the preceding impact and density charts. For lack of a better
description, the designation "Impact Grade" Hickory refers to a
source of regional varieties selected according to subspecies from a
small area in the Central Appalachians where trees are selected that
yield wood with properties suitable for martial art equipment. Not
only is the material unique mechanically, it is also handled much
differently than cabinet grade lumber. Common grades of commercial
hickory are grouped together. Commercially distributed hardwood is
usually kiln dried and hickory, which is difficult to dry, is sawn
into into standard 3/4" planks which allow accelerated dry kiln
schedules. These thinner planks include (mechanically) inferior
species of Northern and Western hickories with the added risk of
structural damage caused by faster drying schedules. This special
stock however, is cut into thicker slabs of the most premium material
from a specific geographical area and slowly air dried. This resulting
"Impact Grade Hickory" is either bone white or light reddish in
color. It has a flat, graceful grain structure and a smooth texture
with good density. Its shock strength exceeds all native and exotic
species including the commonly used Japanese White Oak (Shiro
Kashi). While Oaks appear to become brittle with age, Weapon Grade
Hickory retains its toughness. Although heavy contact with very hard
materials will cause some denting, normal practice with similar
weapons will just create an unobjectionable patina. Even after years
of heavy use, it is unlikely to snap into dangerous pieces. Ideally,
the best Dojo choice would be the uniform use of this material for
paired practice. It's safe, strong, attractive and comes from a
domestic managed resource. Just as Kashi is the only wood used in
Japan for practice weapons, American martial artists can look to this
specially graded hickory as the optimal choice.
Laminated Rosewood Composite (LRC)
LRC refers to a limited, premium grade classification of densified
hardwood composite. Made by laminating very thin layers of imbued
birch veneer under enormous pressure, it has a stunningly beautiful
dark Rosewood color with black highlights, is totally stable and takes
a mirror finish.Weapons of LRC have several notable benefits. With a
specific gravity of 1.3, its extremely high density and hardness make
it ideal for smaller weapons where those qualities are so
desirable. It comes from domestic sustainable sources and is an
excellent substitute for rare tropical varieties. Since the
intersticial spaces and microscopic conduits of the wood are filled
with resin, there is little if any exchange of atmopheric moisture and
hence no warpage. When skillfully worked, it holds perfect detail and
when polished and buffed, will take a mirror like shine without any
additional surface treatments. Because it is extremely dense, bokken
made of LRC can achieve both the weight, proportion and balance of a
live blade. It has excellent physical properties overall and, in the
case of bokken, approaches the closest interpretation possible of a
sword. It is however, an engineered material with properties different
from natural wood and LRC items should be treated more like live edged
weapons than those of natural wood. Since the material does not dent
easily, it gives the impression that it is much stronger than any
natural wood. As the tests show however, it's strength exceeds many
of the strongest natural woods but not immensily so. It tends to be
edge sensitive and an accidental drop onto concrete, which would just
dent most natural woods may cause a more serious chip in the composite
material. While there have been many natural wood bokken destroyed
when hit with a composite weapon and at least one live steel blade,
there have also been a few composite weapons broken and a few
instances where a glancing blow at the very end of the point damaged a
composite bokken. For these reasons, the LRC is not recommended for
paired work involving contact but better reserved for suburi
(individual) practice, silent sword techinques, presentation or other
special situations.
The last consideration, as it relates to paired practice may be said
of any of the very hard and dense materials in general: In a practice
situation, many students use equipment that fits their means and their
experience. Very hard and heavy wood will certainly do significant
damage to the budget oriented weapons that many beginning students
start out with. In the interests of safety and good judgement, it is
best to engage in daily paired practice with materials that do not
cause unnecessary damage to a partner's equipment.
African Ebony
Several tropical hardwoods including African Ebony are extremely hard
and heavy but without notable impact strength. Also known as Cameroun
and Gabon Ebony, this wood is jet black with occasional grey striping
and is the familiar black wood formerly used on piano keys. Because of
its density, outstanding hardness and ability to hold detail, it is
excellent in small hand held weapons used to apply pressure. Along
with other wood of tropical origin, Ebony comes from sources that
aren't necessarily well managed, should be considered a limited
resource and used judiciously.
Honduras Rosewood
There are several species of natural Rosewood with excellent density,
strength, dent resistance and overall physical properties. Honduras
Rosewood is usually a dark reddish tan sometimes with prominant
streaks of black and purple. It has a beautiful, coarse swirling grain
structure with color patterns varying from reserved to startlingly
bold. Rosewood is not often available from sustainable sources in
pieces suitable for solid construction larger items. Smaller Tanto,
Kobuton, Yawara and similar works are often possible. Bokken and Jo of
natural Rosewood are highly desirable and extremely rare. This
material, like other tropical woods is not recommended for daily
practice or casual use due to its scarcity and unique character.
Pau Ferro
South American Pau Ferro (Ironwood) has a beautiful dark tan color
often including black streaks and graceful dark figure patterns. It
has fine, dense grain with a very smooth surface texture. Pau Ferro,
an exceptional and rare tropical wood, is occasionally available in
pieces thick enough for solid piece bokken and jo and it makes
excellent blade sections for Yari and Naginata intended for
presentation and solo practice.
Purpleheart Wood
Purpleheart is available in thick pieces which allow for the
construction of largest and longest solid piece weapons. It is
sometimes possible to obtain it from managed sources and has some
outstanding properties making it especially suitable for staff type
weapons like jo, bo etc. It is very hard, and usually displays a
straight, uniform grain structure with a somewhat coarse texture. It
turns to a clear, brilliant violet upon exposure to light.
Purpleheart is extremely stable and lends itself to long, slender
weapons where a less stable material would usually develop noticeable
warpage. Because it is extremely stiff in comparison to its weight, it
gives the user an energetic feel of returning energy rather than
absorbing it and for these reasons, could be considered a
"conditional wood" - an excellent choice for some situations.
Coromandel Ebony
Also known as Macassar Ebony, this exceptional wood deserves special
consideration among the natural woods available for the construction
of wooden swords, staffs and martial art weapons. Because of its
superb character, it conveys a unique and unmistakable feeling of
presence. Coromandel is strong, hard, has a ideal weight with a fine
dense texture. If skillfully shaped and finished, an alive almost
reptilian quality emerges with predominantly black with tan figure
patterns and occasional subtle but surprising hints of green and other
colors. It is arguably one of the most beautiful of all woods.
Upon reading this description, it may be tempting to conclude that a
fine weapon of Coromandel Ebony is the optimal personal choice for the
serious student of the martial arts. Its unrestricted use however,
would actually be inappropriate. Acquiring unique and rare weapons of
limited natural resources often reflects the enthusiam of aspiring
students where, due to the cost and scarcity of this material, is best
reserved for special situations - a gift perhaps to a senior
instructor from an appreciative dojo.
Osage Orange
No discussion of wood, selected for weight and strength, is complete
without mention of Osage Orange, an unusual North American hardwood
with a unique heritage. Indigenous to the American Southwest, the wood
has a superb strength and was highly prized by Native Americans for
archery bows and is still coveted by traditional bowyers. When freshly
cut, it has a startling and unlikely bright yellow color which slowly
turns to a subdued orange tan. The tree does not produce much of the
dense, straight grained wood which has good mechanical
properties. High quality lumber is very rare but the tree is certainly
not endangered. Other studies of shock strength sometimes rate Osage
Orange as the strongest of all woods. When used in longer weapons for
paired practice it absorbs energy upon impact with a surprising
springy feel.
Under the name Kingfisher Woodworks,
James Goedkoop has produced thousands of practice weapons for
aikido practice and the sword related martial arts.
This article was first printed in the May/June 1999 edition (Issue
#63; Vol 13, No. 3) of Aikido Today
Magazine and is reprinted with their permission.
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