A glossary of terms related to hardwood species
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.
Compressive Strength Parallel to Grain:
Maximum stress sustained by a compression parallel-to-grain specimen having a ratio of length to least dimension of less than 11.
Compressive Stress Perpendicular to Grain:
Reported as stress at proportional limit. There is no clearly defined ultimate stress for this property.
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.
A term that describes whether a section of wood will resist changes in volume with variation in moisture content (other term: movement in performance).
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.
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.
An excessive local accumulation of resin or gum in the wood.
Generally defined as resistance to indentation using a modified Janka hardness test, measured by the load required to embed a 11.28 mm (0.444 in.) ball to one-half its diameter. Values presented are the average of radial and tangential penetrations.
A description applied to woods from deciduous broad-leafed trees (Angiosperms). The term has no reference to the actual hardness of the wood.
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.
In the impact bending test, a hammer of given weight is dropped upon a beam from successively increased heights until rupture occurs or the beam deflects 152 mm (6 in.) or more. The height of the maximum drop, or the drop that causes failure, is a comparative value that represents the ability of wood to absorb shocks that cause stress beyond the proportional limit.
Modulus of Elasticity:
An imaginary stress necessary to stretch a piece of material to twice its length or compress it to half its length. Values for the individual species are given in megapascals (MPa – equivalent to N/m2), and are based on testing small clear pieces of dry wood.
Modulus of Rupture:
Reflects the maximum load-carrying capacity of a member in bending, and is proportional to maximum moment borne by the specimen. Modulus of rupture is an accepted criterion of strength, although it is not a true stress because the formula by which it is computed is valid only to the elastic limit.
Moisture Content (M.C.):
The weight of water contained in wood expressed as a percentage of the weight of the oven dry wood.
Pith-like irregular discolored streaks of tissue in wood, due to insect attack on the growing tree.
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.
Quarter-sawing 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. Quarter-sawn boards are popular for decorative applications such as cabinet faces or wainscoting. They will expand and contract less than boards sawn by other methods.
Rift-sawing at a 30-degree or greater angle to the growth rings produces narrow boards with accentuated vertical or “straight” grain patterns. Rift-sawn boards are often favored for fine furniture and other applications where matching grain is important. This type of lumber is available in limited quantities and species.
The outer zone of wood in a tree, next to the bark. Sapwood is generally lighter than heartwood.
Shear Strength Parallel to Grain:
Ability to resist internal slipping of one part upon another along the grain. Values presented are average strength in radial and tangential shear planes.
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.
Separation of the fibers in a piece of wood from face to face (other term: end-split).
Materials used to impart color to wood.
Tensile Strength Perpendicular to Grain:
Resistance of wood to forces acting across the grain that tend to split a member. Values presented are the average of radial and tangential observations.
Determined by relative size and distribution of the wood elements. Described as coarse (large elements), fine (small elements) or even (uniform size of elements).
Distortion in lumber causing departure from its original plane, usually developed during drying. Warp includes cup, bow, crook and twist.
The weight of dry wood depends upon the cellular space, the proportion of wood substance to air space.
Acacia wood species are known for their hardness and durability. In New Kingdom Egypt, an acacia species was a type of wood used in the finest mummy coffins. A Hawaiian species, Acacia koa, aka koa, was commonly used in contemporary furniture, but the fast-growing Australian blackwood has supplanted it because of environmental concerns. It’s a highly decorative, lustrous, and usually straight-grained acacia wood. Acacia is commonly used in .
Most famously used in the construction of major league baseball bats, ash wood has an excellent strength-to-weight ratio. Its genus is Fraxinus, but the common name, ash, derives from the Old English word for “spear,” as ash was the preferred wood for spear shafts. White and black ash are the species commonly used in furniture. This is a straight-grained, light-colored hardwood that finishes beautifully.
Beech’s most innovative use as a furniture wood was in the 19th century, when Michael Thonet formed it with steam to create bentwood furniture. Beech is also famed for its use in mid-century modern Scandinavian design. A heavy and strong wood, beech is tight-grained and pale reddish-brown in color. It’s commonly used in the crafting of stools and chairs.
Yellow birch (Betula alleghaniensis) is one of the most commonly used furniture woods in the U.S. It’s heavy, hard, and strong, with a close grain that allows for beautiful wood finishes. Birch is often used as a lower-cost alternative to hardwoods such as mahogany, walnut, and maple. It’s also commonly used in the production of plywood (see our engineered wood entry).
Eastern red cedar is a softwood used in the construction of storage chests, closet linings, and drawer bottoms, where its aromatic oils provide natural resistance to moths and insects. Fine-grained and knotty, this species is beautifully colored, with reddish-brown heartwood and whitish sapwood. Rustic furniture is more often made from northern white cedar, a durable, straight-grained wood with white sapwood and pale brown heartwood.
American black cherry (Prunus serotina) has been prized for its beauty and woodworking qualities for centuries, most notably in Colonial-era cabinets. Distinguished by its rich coloring and lustrous appearance, this species has a red/reddish-brown heartwood and creamy white sapwood. It’s a straight-grained wood with distinctive gum pockets. Cherry wood is photosensitive and will darken with age and light exposure.
Engineered wood is the broad term for composite or multi-layer man-made woods, including medium density fiberboard (see our MDF entry), plywood, and particle board. Engineered woods can actually provide greater strength and shrink-resistance than real woods, with a natural appearance at a lower cost. Their use of materials such as sawmill waste and scrap wood makes them an eco-friendly choice as well.
True mahogany wood is still used in the manufacturing of fine furniture and musical instruments, but for environmental reasons, contemporary mahogany furniture is usually made from reddish-brown mahogany alternatives. Meranti, a species of Shorea, is commonly known as Philippine mahogany. Sapele and okoume (see our okoume entry below) are two popular African hardwood species that offer good value and durability as mahogany alternatives.
Medium density fiberboard is an engineered material made of waste wood fiber, chips, sawdust, etc., bound together with resin adhesive and formed into hard panels using high heat and pressure. MDF is inexpensive, strong, and durable, with smooth surfaces and uniform texture, making it an ideal material for shelving and bookcases.
Red and white oak are the most widely used hardwoods in American furniture thanks to their outstanding strength, durability, and hardness. Oak is a straight-grained, open-pored wood with a coarse texture. Oak’s decorative appeal lies in its distinctive grain patterns and excellent finishing properties. Oak is most often used in the construction of traditionally styled wood furniture.
Okoume is an imported hardwood that’s commonly used as an alternative to mahogany. Also known as okoume mahogany or gaboon, it features a generally reddish-brown heartwood and straight grain, with a mahogany-like texture. In addition to furniture construction, okoume is widely used in the manufacturing of marine plywood for boatbuilding, thanks to its light weight and excellent strength-to-weight ratio.
Many species of pine are used in the construction of furniture, including ponderosa pine and eastern and western white pine. White pine is a softwood that’s lightweight and straight-grained. Creamy white to pale yellow in color, white pine lacks a distinctive grain pattern versus other woods, but knotty pine is commonly used to give a distinctive appearance to rustic and other traditional furniture styles. Pine can be given a to produce varying wood colors, or may also be painted.
Yellow poplar is a great value among furniture woods. Used in both stained and painted furniture (often as an alternative to white pine), this pale, lightweight wood is less expensive than most hardwoods. Though not the strongest or hardest of woods, poplar is very easy to work with and finish. It features a white sapwood and yellowish-brown heartwood, a straight and sometimes woolly grain, and a fine texture.
Reclaimed wood refers to timbers or logs that have been salvaged from barns, warehouses, railroad ties, farm implements, old bridges, and other structures, or from nature itself in the case of driftwood or “sinker logs.” Reclaimed wood offers both ecological and aesthetic benefits for furniture or home building. In addition to its natural weathering, reclaimed wood often provides quality, density, and/or color that’s unavailable in newly harvested wood species.
Historically significant as a valuable source of latex before the invention of synthetic rubber, the Para rubber tree (Hevea brasiliensis) has since become an important source of eco-friendly plantation hardwood. The rubberwood is harvested at the end of the tree’s productive phase, clearing room for new trees. Rubberwood is strong and very durable, and is often used in paint-grade applications.
According to the Trade Practice Rules for the Household Furniture Industry established by the Federal Trade Commission in 1963, solid wood is a label which “means exposed portions of both frames and panels are made of solid lumber, not veneers or plywood.” This excludes unexposed surfaces, i.e. drawer sides, for which other woods may be used.
Native to south and southeast Asia, teak is an extremely strong and durable hardwood. It’s yellow to golden-brown in color and may be straight-grained or strongly figured. Teak wood is commonly used in outdoor furniture because of its resistance to rot, insects, and water, but reclaimed teak has become a popular material choice for high-quality indoor furniture.
A versatile hardwood that works easily and finishes beautifully, black walnut is a preferred wood for high-end cabinetry, gun stocks, and highly figured veneers. Strong yet relatively lightweight, walnut has chocolate brown heartwood and white sapwood. Though often straight-grained, walnut is valued for its distinctive figures, including burls and crotches. As a furniture wood or veneer, it’s a beautiful choice for home libraries and offices.