Deterioration of Grenadilla* Instruments - Part 2: Can We Communicate Clearly About the Problem?

Written by Larry R. Naylor

Part 2: Can We Communicate Clearly About the Problem?

Now that we have objectively validated the problem, and that problem involves wood deterioration, we need common vocabulary or jargon to discuss it further. Towards that end, let us review some rudi­ments from botany.

Wood: Botany Review

Plants, like all livings things, consist of cells. While there are different kinds of plant cells, the physiology of cells is essentially the same. Cell walls surround and border each cell. In wood, cell walls consist pri­marily of long fibers called cellulose. In a matter of speaking, cellulose is the “skin” of a plant cell. Cells join, wall to wall — and there are different kinds of joined cells — each with a specific botanical func­tion. Fluids can pass among cells just under the bark by a process called osmosis.

We can conceptualize wood as a bundle of soda straws, where each straw represents end-to-end cells of cellulose. When young, these cells, called xylem, are actively involved with the respiration and growth of the tree; they carry water and minerals from the roots to the rest of the tree, and their structural func­tion is only secondary. As xylem ages, it begins to lose its transport role. Cell walls become thick and fill with lignin and hemicelluloses. This process is akin to gluing straws together, thus producing a structure of greater strength. We call the product of this lignin deposition, “wood.” Moreover, at this stage, the only function “wood” serves is providing structural strength to the tree.

There are also specialized cells called “phloem,” and still others, “cambium,” which produce new xylem and bark during a growing season. The more rapid production of xylem during the spring generates new cells that are less dense than cells produced near the end of the growing season. This accounts for, as seen in a cross section of a log, what we label as annual growth rings. Tropical hardwoods contain much more lignin within cell walls than woods from temperate climates.

Cutting Patterns and Billets

Over time, we have learned that wood from certain trees is better suited for wood­winds. Although museums are filled with woodwinds made from all manner of wood, nowadays woodwind bodies are cut predominantly from three tropical [equatorial] trees: cocobolo, rosewood, and grenadilla (the latter, mpingo, a.k.a. African blackwood, or from the French, ebony).

After crosscutting a log, it is ripped into billets of various dimensions and lengths. For soprano instru­ments, “body” billets measure roughly 2 X 2 inches, by the needed length. After quality-oriented sorting, the billets are aged or seasoned. The two-fold purpose of seasoning is to dehydrate the billets, and to allow internal stresses to balance. At some point in the seasoning process, manufacturers may bore a rough, undersized hole through the center of the billets, then let them age further. Aging time varies per manufacturer. It is quite common to season billets ten or more years. Contrarily, if one were to insuffi­ciently season the wood, the billets would be unstable in many climates. Such less than ideally seasoned billets are very prone to cracking.

Figure 2.1 below represents a cross section of an irregular log ripped into nine billets; the heavy vertical and horizontal lines represent basic saw cuts in the log; the figures are not drawn to scale. In this example, getting good, usable wood for soprano billets means this log would have to be greater than six inches in diameter. This cutting pattern produces two different grain patterns of wood; one billet of central heartwood and up to eight billets of regular heartwood, regardless of the log’s diameter.

Figure 2.2 depicts a cross-sectioned, quartered log. This log would have to be greater than four inches in diameter to produce soprano billets. Moreover, this pattern would not yield a central heartwood billet.

Figures 2.3 and 2.4 represent cross sections of the two types of cutting patterns. Note that the annular grain in the central heartwood example form concentric rings while the grain in the other billets runs “corner” to diagonal “corner.” Typically, manufacturers use central, heartwood billets when making Oboes, and English Horns, while Figure 2.4 type wood typically becomes Clarinets.

Most grenadilla billets are not central heartwood. Yet, wood used to manufacture world-class instru­ments represents the best available wood in the marketplace. The two types of billets, as in Figures 2.3 and 2.4, are simply differ­ent. They have different physical characteristics and they react differently to the environment, saliva, and age.

Now that we have a more common vocabulary, let us apply our renewed knowledge of wood to the problem of deteriorated grenadilla instruments.