What Makes Wood Beautiful?
If you've been working with wood for very long, you realize that each species has different characteristics and appeal. You probably know, too, that even a pair of boards taken from two logs of the same species may not look exactly alike. That's because color, luster, texture, grain, and figure all come into play for a species' visual appeal. And it's one or more of these characteristics that put a high value on the most favored hardwoods used for decorative purposes. Now you'll learn just what they are.
Color covers the palette
In hardwoods, color occurs naturally across a wide range. There are purples, yellows, oranges, almond tones, browns, cinnamons, and shades of red. And color plays a major role in determining the final use of the wood. East Indian rosewood's decorative color makes an attractive turned bowl. But a nearly colorless wood, such as birch, makes a good mixing spoon.
Wood has color due to infiltrates that interact with the cellulose of its cell walls and the lignin that bonds them together. These infiltrates are soluble materials (sometimes called extractives) that a tree draws from the soil where it grows. Various species react to the infiltrates in different ways, thus creating contrasts among them. But that's also why even within a species the wood's color can vary. Walnut harvested from the cool limestone bluffs of northeast Iowa, for instance, will differ in color from that grown in central Kansas.
Freshly sawn green wood from a tree also can change color when exposed to air and light, sometimes drastically. South American purpleheart turns from light brown to purple. Osage-orange is a bright yellow-orange when first cut or planed, but shortly turns brown. Some woods, such as teak, fade under strong light but darken by moderate light. The moist heat of kiln drying will change a wood's color, too. As an example, the lighter color of walnut's sapwood evens out in a kiln to match the darker heartwood.
Luster in the light
A wood that has luster reflects light from its cell walls and appears to have a natural sheen. But any infiltrates in a wood's cell walls that give it color reduce its luster. Because of this, light-colored hardwoods will have luster, as does the light sapwood of darker hardwoods. Lack of luster, however, does not mean that a wood won't take a high polish when finely sanded, then buffed. Finishing also adds luster.
In general, quartersawn wood has more luster than flatsawn, as with white oak. The ray flecks in white oak exposed by this manner of cutting reflect light. Too, woods with lots of figure, such as curly and fiddleback maple' display added luster due to the cell walls' changing angle to the light.
Texture to feel
When wood is said to be "coarse" grained or "fine" grained, it's a reference to its texture. And a wood's texture depends on the relative size and variation of size in its cells and the width and abundance of its rays. You actually can feel the difference between fine-textured wood with small cells and thin rays and coarse-textured wood with wide vessels and broad rays. Red oak, for example, rates as coarse-textured, while hard maple is fine-textured. Walnut, however, is moderately coarse-textured, while holly is very fine-textured.
Texture is only sensory. A wood's texture has little to do with how it saws or machines.
Grain follows direction
"Grain" is a term that's often misused. It does not refer to the natural pattern seen on the surface of wood. That's figure. Technically, grain means the orientation of the wood cells. Under that definition, there are six generaltypes of grain:
- Straight grain indicates that the cells and fibrous components run completely or nearly parallel to the vertical plane of the tree trunk and the log that came from it.
- Irregular wood grain implies irregular variations from the parallel orientation of the grain to the log. This most often happens around knots.
- Diagonal grain describes what results when an otherwise straight-grained log is not sawn parallel to its vertical axis—in other words, angled sawing.
- Spiral grain happens when the cells and fibers grow in a left or right twisted configuration around the trunk of a tree.
- Interlocked grain occurs when each successive layer of new growth on a tree runs in a different direction.
- Wavy grain is produced when the direction of the fibers alternate so that a board's surface looks like a washboard, as with the figure pattern of curly maple.
Figure in the patterns
Although some grain configurations in wood frequently do result in figure, the word describes the pattern that often occurs when several features interact, including irregular grain, rays, color deposits, and growth rings. Irregular grain in crotches and burls causes "feather" figure, "plum-pudding" figure, and others. Interlocked grain promotes "ribbon" figure and "bird's-eye." Wavy grain creates "fiddleback" or "tigerstripe" figure.
Highly sought and expensive figured veneers are regularly manufactured by slicing or peeling a log with irregular or interlocked grain in a special manner. Changing the angle of cut enhances the irregularities and yields special effects. It's the same with lumber; quartersawing a regular-grained wood sometimes results in figure pattern, again as with white oak and its ray flecks.
Another term used by woodworkers to describe what loosely could be called figure pattern is "character marks." This refers to naturally occurring ingrown knots, "tracks" left by insects in the living tree, "bird peck," and other signs that make the wood appear less than perfect. However, a skilled craftsman employing wood with character marks in a project can literally turn a sow's ear into a silk purse.