Wood Samples

A Glossary of Wood Terms

Checks: Longitudinal separation of the fibers in wood that do not go through the whole cross section. Checks result from tension stresses during the drying process.

Density Weight per unit volume. Density of wood is influenced by rate of growth, percentage of late wood and in individual pieces, the proportion of the heartwood.

Dimensional Stability: A term that describes whether a section of wood will resist changes ]=in volume with variation in moisture content (other term: movement in performance).

Figure: The pattern produced in a wood surface by annual growth rings, rays, knots, deviations from regular grain, such as interlocked and wavy, and irregular coloration.

Grain: The direction, size, arrangement, appearance, or quality of the fibers in sawn wood. Straight grain is used to describe lumber where the fibers and other longitudinal elements run parallel to the axis of the piece.

Gum Pocket: An excessive local accumulation of resin or gum in the wood.

Hardwood: A description applied to woods from deciduous broad-leafed trees (Angiosperms). The term has no reference to the actual hardness of the wood.

Heartwood: The inner layers of wood in growing trees that have ceased to contain living cells. Heartwood is generally darker than sapwood, but the two are not always clearly differentiated.

Moisture Content (M.C.): The weight of water contained in wood expressed as a percentage of the weight of the oven dry wood.

Pith Flecks: Pith-like irregular discolored streaks of tissue in wood, due to insect attack on the growing tree.

Plain-Sawn: Plain-sawn hardwood boards are produced by cutting tangentially to a tree's growth rings, creating the familiar "flame-shaped" or "cathedral" pattern. This method also produces the most lumber from each log, making plain-sawn lumber a cost effective design choice. Plain-sawn lumber will expand and contract more than boards sawn by other methods. However, it performs just as well when properly kiln-dried, when the job site is properly prepared and when the hardwood products are acclimated to the home before installation. (See Managing Expansion & Contraction, Moisture Content)

Quartersawn: Quartersawing means cutting a log radially (90-degree angle) to the growth rings to produce a "vertical" and uniform pattern grain. This method yields fewer and narrower boards per log than plain sawing, boosting their cost significantly. Quartersawn boards are popular for decorative applications such as cabinet faces or wainscoting. They will expand and contract less than boards sawn by other methods.

Sapwood: The outer zone of wood in a tree, next to the bark. Sapwood is generally lighter than heartwood.

Shrinkage: The contraction of wood fibers caused by drying below the fiber saturation point (usually around 25-27% M.C.). Values are expressed as a percentage of the dimension of the wood when green.

Specific Gravity: The relative weight of a substance compared with that of an equal volume of water. The S.G. of wood is usually based on the green volume and oven dry weight.

Stain: Materials used to impart color to wood.

Texture: Determined by relative size and distribution of the wood elements. Described as coarse (large elements), fine (small elements) or even (uniform size of elements).

Warp: Distortion in lumber causing departure from its original plane usually developed during drying. Warp includes cup, bow, crook and twist.

Weight: The weight of dry wood depends upon the cellular space, the proportion of wood substance to air space.

Work to Maximum Load in Bending: Ability to absorb shock with some permanent deformation and more or less injury to a specimen. Work to maximum load is a measure of the combined strength and toughness of wood under bending stresses.