Historically, societies have placed a high value on the surface and finish of all things made. Beyond furniture’s visual appeal, surfaces are felt; they absorb and emit odor; they need to be cleaned and maintained; and most surfaces will wear, scratch, and fade. Many common materials such as wood, stone, and natural fabrics are porous and require sealers to protect and enhance their visual appeal.
Surface quality is a general term that describes the visual and tactile characteristics of a material’s surface. Descriptive characteristics of unfinished wood include figure, grain, and texture. Descriptive characteristics of finished wood include depth and luster. Metal can be polished or given a patina, and genuine leather has a "soft hand."
A material’s unique cellular structure will influence its surface attributes. The arrangement of its atoms will differentiate its visual and performance characteristics, such as its absorptive or impervious aspects, its brittle or resilient nature, and its transparent or opaque attributes.
A textile with open-cell cellular structure such as cotton will breathe well. A painted, open-grain wood may be susceptible to peeling when changes in humidity cause the grain to rise and expand. Metal can tarnish, glass can slump, and wood will darken over time.
Visual Aspects of Finished Wood Surfaces
Depth is a visual quality that depends on the process and type of finish used as much as it does on the wood species itself. Wood surfaces with an open cellular structure can be enhanced with an oil finish. Open-celled wood, when finished with oil or a lacquer, can be enhanced by the natural cellular structure and the depth of penetration by the finish. In the past, the first finish coat applied to wood furniture, casework, or flooring, was often thinned using mineral spirits to allow for deeper penetration. This, in turn, created a greater sense of visual depth in the wood’s finish.
The ability of finished wood to reflect and refract light gives luster to its surface. Luster is a visual quality that becomes apparent only when wood is finished. Compact and smooth woods such as curly or hard maple and special qualities in grain such as ribbon curl, when finished, can reveal a remarkable luster (Figure 7.26). Luster and color in finished wood are responsive to and dependent on one’s viewing angle, the characteristics of the grain, and the source of the light. Walk around a finished table and study the visual transformation that occurs as the
viewing angle and orientation change. It is remarkable how much variation can be perceived in the luster and color of finished wood.
Visual Aspects of Unfinished Wood Surfaces
Figure is a term that describes grain anomalies. The natural characteristics of wood (i. e., medullary rays, growth rings, color variation, texture, knots, and abnormalities) all contribute to the characteristics of wood’s figure. Imperfections such as stresses during growth and disease also contribute to wood’s figure. Storing, drying, and seasoning lumber can affect a wood’s grain. The formation of small checks, splits, or flaws on the surface of lumber can result from uneven seasoning. This is known as checking. Various types of figuring in wood include: ribbon stripe, flake, wormholes, block mottles, bird’s eye, fiddle-back, quilted, curly grain, tiger, crotch, and burl.
Grain is the direction of the fibers relative to the long axis of the tree. Cut boards have three categories of grain based on location—face grain, edge grain, and end grain. In lumber where growth has been even and the cell structure is in line with the main axis of the tree, the wood will be straight-grained and relatively easy to work. Quarter-sawn straight grain results in uniform and stable lumber. Depending on how the tree is milled, wavy grain can give a rippled effect on tangential surfaces, while unusual growth malformations in the cambium layer of maple cause the cells to grow into a series of small, tight cellular structures called bird’s eye.
The term grain is also used to describe the way wood is worked. Sawing, planing, and sanding are typically done with the grain. Cuts made at 90 degrees to the grain are known as cross-cuts and often require finer blades for quality cuts.
The texture or feel of a wood’s surface is the result of the cellular structure of the material. Lumber that has wide vessels or open cells, such as red oak, is considered coarse-textured, whereas lumber with closed, porous cells and densely spaced cells is considered to be fine – textured (like the mahoganies). Softwoods are not open-celled. Their cells have a small diameter. As a general rule, think of softwoods as a bundle of tiny solid rods and hardwoods as a bundle of tiny open straws. The texture of softwoods results from the difference between early and latewood zones. When these zones are strongly marked, as in Douglas fir, the texture is considered uneven, and when there is little contrast between the zones, as in sugar pine, the wood is considered evenly textured.