In my last column, responding to questions from Alec Brainerd of Artisan Boatworks in Rockport, Maine, I compared the properties of American mahogany (Swietenia macrophylla) with some alternative woods, namely African mahoganies, sapele, sapo, and the lauans (also known collectively as Philippine mahogany). Alec also asked, “How exactly can one identify true mahogany so as not to be confused with Philippine or other species?” This is a tougher question, but one I addressed in 1983 (WB No. 55). With some modifications, I will repeat the information in that column here. In addition to the above woods, I am adding Spanish cedar (Cedrela odorata), a Latin American wood that resembles mahogany and is often used by boatbuilders.
Also, I need to add a correction. In my previous column I interpreted the wood that Alec called “sepo” as “sapo.” Upon reflection, sepo is much more likely “sipo”; both would be pronounced the same. Sipo is Entandrophragma utile , and its more common trade name is utile. My faulty interpretation points out the serious flaws in using common names for woods.
The procedure used by wood scientists for identifying wood involves cutting very thin sections and examining them under the microscope. This definitive method is the only one that holds up in a court of law. An intermediate method requires only the use of a hand lens (preferably 10X or higher magnification) and a sharp knife or razor blade to smooth the surfaces of wood. I recommend Bruce Hoadley’s book Identifying Wood (The Taunton Press), as it has great color photos of smoothed transverse surfaces, also known as end surfaces, of North American woods and a few tropical woods. Obtaining a smooth transverse surface is critical to the successful observation of details with the hand lens.
Hand lens identification has distinct limitations, and to become adept at separating a wide range of woods using this technique requires months or years of training and practice. However, the procedure is useful to amateurs if confined to distinguishing a very limited number of species. I will describe here only the following woods:
- Swietenia spp.—American mahogany, also called Honduras mahogany, genuine mahogany, etc.
- Khaya spp.—African mahoganies.
- Cedrela spp.—Spanish cedar, cigarbox cedar, cedro, etc.
- Shorea spp.; Parashorea spp.; Pentacme spp.—Collectively
referred to as Philippine mahogany or lauan, and separately as meranti, red lauan, white lauan, yakal, almon, tangile, etc. - Entandrophragma cylindricum— sapele, penkwa, aboudikro, etc.
- Entandrophragma utile—utile, sipo, okeong, kosi-kosi, etc.
The features that we will use are:
(1) Arrangement of Vessel Pores (transverse surface). This feature can sometimes be seen without a hand lens. The large openings, or pores, seen in the transverse surface of a hardwood may be uniformly distributed across a growth ring (Figure 1), in which case we say the wood is diffuse porous. Or, the largest pores may be concentrated in a band at the beginning of the growth ring (Figure 2), in which case we say the wood is ring porous.
(2) Arrangement of Rays (tangential or flat-sawn surface). Ray tissue is composed of cells with the long axis oriented in the radial direction; and hence, rays appear like spokes on a wheel in a transverse section. This can be easily seen on a smooth end surface of an oak log. On the tangential surface, rays are seen as short, vertically oriented hatch lines. In oak or beech these can be seen with the unaided eye. In many other woods a hand lens is necessary. If these hatch lines are arranged in regular, slightly wavy horizontal rows, we say the wood has storied rays (or contains “ripple marks”). Figures 3 and 4 show storied rays; in Figure 4 the nearly horizontal arrangement is highlighted with white hash lines. Figure 5 shows the random arrangement of unstoried rays.
(3) Presence or Absence of Axial Gum Ducts (transverse surface). Gum ducts are long tubes or ducts that run vertically in the stem and, therefore, are seen as tiny openings or pores on the transverse surface. In the Philippine mahoganies, these pores are embedded in relatively short arcs of parenchyma tissue (consisting of soft, unspecialized, thin-walled cells) and are seen as tiny pores, which are smaller than vessel pores, embedded in whitish tangential arcs of parenchyma (Figure 6).
The key above uses these features to provide some separation among the woods. However, we see that Swietenia is not separated from Entandrophragma cylindricum, and Khaya is not separated from Entandrophragma utile. For these separations, we need to rely on wood color. The color of Swietenia and Khaya heartwood is reddish, pinkish, salmon, or yellowish when fresh, darkening with age to deep, rich red or brown. By contrast, the heartwood of the two Entandrophragma species is medium to dark reddish or purplish brown. Separating old wood among these is more difficult, but planing or slicing a mahogany board should reveal the lighter color. I might also note that Khaya and the lauans are more likely to have ribbon stripe grain pattern than Swietenia or Cedrela.
With some practice, storied rays in Swietenia can be seen without the use of a hand lens, especially in the lighter-colored, faster-growth material (Figure 3). Certain features are best seen on a dry wood surface while others are often clearer if the surface is wetted. Experiment until you achieve the best results. Practice first on well-identified samples, if possible, until you are comfortable that you can recognize the key features. However, if large monetary stakes are riding on the outcome of your identification, I would recommend contacting a reputable wood anatomist for a final verdict. The cost may well be worth it.
This article was originally published in WoodenBoat No. 204, September/October 2008.