|
|
4.
The Wood
Most
bows are made of pernambuco, a wood that comes from Brazil.
In fact, instead of gold, Vespucci (1451-1512) brought home a red
wood from Brazil, that the Portuguese called pao brazil. At the
time, the wood was used in the production of red dye. In Amsterdam we still have the "rasphuis" where female prisoners had to rasp pernambuco. There is an old description of those poor woman with tears running through the dust on their faces.
Originally
the wood came from a region still known as Pernambuco, although
there is no longer a single pernambuco tree there. Today pernambuco
comes from other, more humid parts of Brazil. There the wood grows faster,
and rarely has the quality that was still common in the 19th century.
But when chosen carefully, good pernambuco can still be found.
Other
kinds of wood are also used. Snakewood, mentioned earlier
in connection with viola bows, is primarily used for baroque
bows. In the transitional peiod between the baroque and the
modern, there were experiments with ironwood. Actually, this
is a generic category for a variety of tropical hardwoods, still
known today by a confusing variety of names. I have personally had
few good experiences with ironwood, but it is entirely possible
that several species have the advantages associated with pernambuco.
Cheap bows are often made of brazilwood, which is related
to pernambuco, but clearly makes for inferior bows.
To
be sure, pernambuco too differs signicantly in quality.
It is practically impossible to judge a whole trunk. In any case,
I have so often been disappointed that I have learned to be careful.
When I go through a bundle of wood, I buy 10% at most, usually less.
What I first look at is weight. If the boards are all cut
alike, weight differences are perceptible. The heaviest are the
densest wood. If the grain is relatively straight, it is
worth cutting the board into sticks. The direction of the grain
shows how straight the wood has grown. There are often different
colored stripes in the wood, which can be misleading, because they
may not go in the same direction as the grain, but are much more
conspicuous, although they have no effect on the quality of the
wood.
The
first two criteria are therefore density and linearity. If
one wants to know the density, it suffices to cut off a small piece
and throw it in a glass of water. If it sinks, its specific gravity
is greater than water, which is cause to rejoice. If it floats,
the wood is relatively porous. It can still make a good bow if enough
attention is paid to this in the construction. But a heavy bow
can not be made of light wood. This sounds simple, but it took
me some years of practice to learn.
The
advantage that porous wood often has is its greater elasticity.
This is a difficult concept in principle, but it works like this:
hold on to a stick firmly at one end, lay the other on a firm surface,
e.g., a table, and push on the middle of the stick with the free
hand. What matters is not so much the effort needed to bend the
stick - this has more to do with its thickness - as the way the
stick returns to its original state. This is elasticity. The
elasticity of a given bow depends on the length of the individual
wood fibers, which is hard to judge with the naked eye. A device
developed by G. Lucchi, my former teacher in Cremona, is
useful here. It transmits ultrasound at a certain frequency
through the wood. The faster the ultrasound passes through the wood,
the more elastic it is. This can be misleading, because numbers
are always seductive. But given adequate caution in the interpretation
of the data, the device is a good thing, even though generations
of bow makers managed without it.
If
the wood is very elastic, care is required to keep the bow
from becoming too nervous. If the wood is less elastic, it
should make a stronger bow, with a full camber. The idea is to compensate
for elasticity with more tension. Greater elasticity is surely an
advantage. But it is more important that the concept of the bow
correspond to the quality of the wood.
The
way the stick is cut is extremely important. First, the saw has
to follow the grain of the wood as closely as possible, while
avoiding all possible branches and cracks. Second, one needs to
be aware of how the annular rings are positioned in the stick.
Two
considerations are involved here. The first is the risk of breakage.
All wood splits or cracks at a right angle to the annual rings.
This can be clearly seen in a bundle of firewood. The cracks all
point in a star pattern toward the middle. When wood is split, this
is also done at a right angle to the annular rings. The head of
every bow is higher than it is wide. If the annular rings are horizontal
with respect to the head, the bow should split in a vertical
direction. But that rarely happens, since even a violin bow is two
centimeters thick in this direction.
But when the annual rings are vertical with respect to the head,
the bow breaks across. The width of the head is only five millimeters
thick, therefore the bow breaks more easily in that direction. I
can demonstrate this with a practical example. A few years ago I
copied a very fine Pfretzschner violin bow. The copy was a great
success, save that I overlooked the annular rings. In the original
they lay across the head. In my bow they were vertical with respect
to the head. After about 10 minutes of playing, the head broke off.
The player, a well known violinist, was horrified. Since then I
know that, when the annual rings stand upright, the head has to
be as massive as possible.
Were
the danger of breakage the only question, things would be
easy. Unfortunately there is another problem. The wood is strongest
in the direction of the annular rings. Seen in this perspective,
it would be an advantage if they were vertical with respect to the
head. Or still better, they would correspond to the angle at which
the bow is played, which is not exactly vertical. Violinists and
violists tip the bow slightly to the right, cellists and bass players
to the left. The ideal position of the annual rings is therefore
at an angle to the plane of the bow, with a somewhat horizontal
tilt. In this way the danger of breakage can be minimized while,
at the same time, the full strength of the wood is brought to bear
in the movement of the bow.
Unfortunately,
a straight, highly elastic stick of very dense wood with the annular
rings in exactly the right place is a rare exception. Almost
every stick confronts the bowmaker with imperfect material.
The art is to match the model and design to the wood in such a way
as to minimize the shortcomings of the material. A small
trick, for example: when the annular rings lie at an angle to the
string, but in the wrong direction, the stick can be cut so that
its cross-section is oval rather than round in the playing direction.
This weakens it in the direction of the annular rings, but strengthens
it in the direction the bow is played by the musician.
The
ultimate quality of a bow depends about 50% on the quality of
the stick, but the other half is the use that is made
of a particular piece of wood.
If
one buys fresh wood, this is best left to mature, sawn into planks,
for about seven years. The wood is already dry after about
half a year. But the tensions that exist in every piece of wood,
take very long to sort themselves out. And when one has sawn the
wood into sticks, it has to be lain aiside once again, so that the
tensions can find a new balance.
If
one wishes to ensure that the finished bow will not move any further,
one must allow as much time as possible between different
handlings. The wilder the wood, the longer a stick needs to calm
itself down. Looked at in this way, one can say that a bow needs
at least ten years before it becomes finally ready for use.
|