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The process of allowing seasoned timber to adjust to the humidity and temperature of its final environment before construction, preventing post-build movement.

Two or more wood rays that are closely grouped or fused together, appearing as a single larger ray in cross-section. Characteristic of some species.

The natural process of seasoning timber by stacking it exposed to ambient air flow. Boards are separated with spacers (stickers) to allow air circulation. Much slower than kiln drying but requires minimal energy investment.

A flowering plant (hardwood tree group) whose seeds are enclosed within an ovary, which becomes a fruit or nut.

Having properties that vary with direction. Wood is anisotropic because it behaves differently along the grain versus across the grain.

One year’s worth of wood growth in a tree, typically visible as a single ring on end grain (earlywood + latewood).

Growth regions at the tips of shoots and roots where cells divide rapidly, producing new tissues that extend the plant’s length (primary growth).

Axial parenchyma arranged in continuous tangential bands, creating visible banding in cross-section. An important identification character in species identification.

A pocket or inclusion of bark embedded within the wood, typically caused by damage to the tree during growth that allows bark to become enclosed as new wood grows over it.

A simple cross-grain jig used on the workbench to hold boards for crosscutting or planing, preventing the workpiece from slipping.

The maximum stress wood can withstand in bending before failure, measured as Modulus of Rupture (MOR) in MPa or psi. Critical value for structural members like joists and beams.

An edge cut at an angle other than 90° to the face of the board. Used for mitred joints, decorative edges, and angled fits.

A distinctive figure characterised by small, elliptical patterns resembling eyes. Most associated with Appalachian sugar maple (Fagus grandifolia). Created by the intersection of vertical and inclined grain when quartered.

A figure pattern on quartered timber showing raised, rounded zones resembling blisters, caused by the interaction of grain direction and figure. Common in quilted maple.

An engineered panel with a core of narrow softwood strips edge-glued together and faced on both sides with veneer. Used for shelving and furniture panels.

A bluish-grey discolouration of wood caused by the sapstain fungus Ceratocystis, carried by bark beetles. Affects appearance but not structural integrity. Common in pine.

A unit of volume for measuring hardwood lumber, equal to a board 1 inch thick by 12 inches wide by 12 inches long (144 cubic inches). Formula: (T x W x L)/144.

Moisture absorbed into the cell wall structure itself, chemically bonded to cellulose and hemicellulose. Removal of bound water causes wood shrinkage and dimensional change.

A curvature along the length of a board's face, where the board deviates from a flat plane. The board curves in an arc from end to end.

Bowing is a lengthwise curve along a board’s face (the board arcs like a shallow bow). It is a type of warp commonly caused by uneven moisture content through the thickness or along the length, drying stresses, or grain/runout effects.

Boxed heart (boxed pith) describes a board or timber section that contains the pith/centre of the log. It is higher risk for splitting, distortion, and stress-related movement during drying and machining.

A zone of weakened, brittle wood in the central core of some trees, particularly eucalyptus. Caused by extractive accumulation and cell wall alteration as heartwood forms.

Rounded, abnormal growths on tree trunks or roots with intense, irregular grain patterns. When sliced into veneers, they produce dramatic decorative figures valued in luxury furniture.

A small, flat steel tool with a burnished cutting edge, drawn across wood to remove fine shavings and produce a tear-out-free surface.

A thin layer of living tissue just beneath the bark that produces new wood (xylem) inward and new bark (phloem) outward.

A cant is a log that has been squared (typically by removing slabs) to create flat faces before further sawing. Many mills break logs down into cants first, then saw boards or structural timber from the cant for efficiency and predictable dimensions.

A drying defect where the outer shell of timber dries and hardens too quickly, trapping moisture inside. The stressed shell can split under machining pressure. Often caused by excessively high initial kiln temperatures.

The main structural carbohydrate in wood cell walls. It forms strong microfibrils that provide most of wood’s tensile strength.

Cellulose microfibrils are tiny, strong bundles of cellulose chains in the wood cell wall. Their orientation (microfibril angle) largely controls stiffness and helps explain why swelling/shrinkage happens mostly across the grain rather than along it.

A beveled edge cut at an angle (typically 45°) to remove the sharp corner of a board. Reduces splintering and adds decorative detail.

An optical effect where wood appears to shimmer or change colour when viewed from different angles. Produced by ribbon-stripe figure in interlocked grain, most famously in figured maple.

Surface cracks in timber that extend partially through the wood, caused by the surface drying and shrinking faster than the interior during seasoning.

Cracks that form as wood dries, often starting at the ends (end checks) or on the surface (surface checks) due to drying stress.

A harvesting method where all trees in an area are cut down in a single operation. Most economical method but has significant ecological impacts.

A grading term for premium-grade hardwood lumber free of knots, with the entire heartwood section usable. The highest quality grade.

A wood texture where pores/vessels are small and not prominent, so the surface feels smoother and needs little or no grain filling.

A severe drying defect where the cell structure of wood shrinks unevenly, causing distortion and crushing of cell walls. Particularly problematic in high-density species.

A structural failure caused by compressive overload along the grain, creating buckling or crushing of wood fibres. Visible as a wrinkled or creased appearance.

The maximum compressive load wood can withstand parallel to the grain before crushing. Essential for columns, studs, and load-bearing structures.

Compression wood is reaction wood formed in softwoods on the underside of a leaning stem or branch. It develops under compressive growth stress, often has abnormal structure and higher longitudinal shrinkage, and can cause boards to bow, twist, and move unpredictably during drying and machining.

A method of woodland management where trees are cut to near ground level, and multiple new stems regrow from the stump (stool). Used for sustainable production of poles and small timber.

The traditional sustainable practice of repeatedly cutting trees (such as hazel, chestnut, or willow) at ground level to harvest new shoots, yielding a renewable supply of small-diameter timber.

A curvature along the edge of a board rather than its face. The board deviates from straight when viewed from above, caused by proximity to the pith or tangential shrinkage in flatsawn boards.

Cross-laminated timber (CLT) is an engineered panel made from thick layers of timber boards laminated in alternating grain directions. Cross-lamination reduces directional movement and enables large, stable structural panels.

Cutting wood across the grain (perpendicular to the fibres), typically producing a clean end face and severing fibres rather than splitting between them.

A separation along an annual growth ring, creating a partial detachment of the growth ring from the rest of the wood structure.

A warp where a board curves across its width, forming a shallow ‘U’ shape, typically driven by uneven shrinkage across growth-ring orientation.

A rectangular groove cut across the grain of a board, wider on the bottom than at the top. Used for shelf joints and partition fitting.

Debarking is the removal of bark from a log before sawing. Mills do this to reduce grit/contamination that dulls blades, improve cut quality, and reduce bark content in downstream products.

The breakdown of wood fibres caused by fungal action, typically when moisture content exceeds 20%. Results in loss of strength, discolouration, and eventual structural failure.

The natural ability of certain wood species to resist fungal degradation, largely determined by extractive content, particularly in heartwood. Teak and white oak are naturally decay resistant.

Mass per unit volume. For timber it is usually reported in kg/m³ at a stated moisture content (often ~12% MC).

A hardwood with pores of relatively uniform size throughout the growth ring (no strong earlywood pore band).

Horizontally oriented wood rays that have been widened or expanded. Often seen in quarter-sawn timber as distinctive figure elements.

Dimensional stability is how little (or how much) a piece of wood changes size as moisture content changes. It depends on species shrinkage values, T/R ratio, cut angle, board width, moisture range in service, finish, and construction method.

A interlocking woodworking joint consisting of trapezoidal pins and tails, creating a strong mechanical bond without adhesives. Cornerstone of fine cabinetmaking.

The speed at which timber loses moisture during seasoning. Varies by species, thickness, and initial moisture content. Ring-porous hardwoods typically dry faster than diffuse-porous species.

Drying stress is internal stress created when wood dries unevenly, producing moisture gradients between shell and core. It can lead to checking, honeycombing, and case hardening if not managed during drying and conditioning.

Wood formed at the start of the growing season, typically lighter and less dense (with larger cells).

Solid wood panels created by joining narrow strips of boards edge-to-edge with adhesive. Also called butcher block or glued-laminated panels.

End checking is cracking that starts at a board’s ends because moisture leaves end grain much faster than face grain. It’s reduced by end-sealing logs/boards soon after sawing and by controlling early drying conditions.

The surface produced when wood is cut across the fibres, exposing the ends of cells.

Cracks that originate from the ends of timber boards and run parallel to the grain, caused by rapid moisture loss from the exposed end grain.

End-sealing is applying wax, paint, or a commercial sealer to the ends of logs or boards to slow end-grain moisture loss and reduce end checking during drying.

Engineered wood is wood-based material made by bonding layers, veneers, strands, fibres, or particles (e.g., plywood, MDF, CLT). Engineered construction reduces or redistributes anisotropic movement, making panels far more dimensionally stable than solid wood.

The stable moisture content that wood achieves when it matches the surrounding air conditions. Reaching equilibrium is the goal of proper seasoning.

The moisture content at which wood neither gains nor loses moisture from the surrounding air. This balance depends on the relative humidity and temperature of the environment. EMC varies by region and season.

First and Seconds — the highest grade in the NHLA hardwood lumber grading system. Minimum clear-face yield of 83-1/3% (FAS) or 83-1/3% plus small defects (1F).

A combined NHLA grade for hardwood lumber meeting either FAS or FAS 1F standards. FAS requires 83-1/3% clear face; 1F allows small defects on the best face.

The moisture content (approximately 25-30%) at which all free water has been removed but cell walls remain fully saturated. Below this point, wood begins to shrink.

Fibre saturation point (FSP) is the moisture content at which the cell walls are fully saturated with bound water but the cell cavities (lumens) contain no free water. Below FSP, changes in bound water cause shrinkage and swelling; above FSP, dimensional change is minimal.

Long, thick-walled cells (especially prominent in hardwoods) that provide much of wood’s mechanical strength.

A pronounced ribbon-stripe figure caused by interlocked grain, typically seen in quartered timber. Named for its use on violin backs. Common in sycamore, maple, and eucalyptus.

The pattern of light and dark areas on the surface of wood, created by growth rings, rays, knots, grain deviations, and colour variations. Determines the decorative value of timber.

A film-forming finish is a coating that creates a continuous surface layer (e.g., varnish, lacquer, paint). It slows moisture exchange between wood and air, reducing the rate of movement (but not stopping it).

Flat-sawn (also called plain-sawn) describes boards cut so the growth rings are roughly parallel to the wide face. Flat-sawn boards often show cathedral grain and usually have greater tangential movement across their width, making them more prone to cupping than quarter-sawn boards.

Boards sawn so the growth rings are roughly parallel to the wide face (typically 0–30° ring angle).

The planning and implementation of practices to maintain and enhance the health, productivity, and value of forest lands for various purposes.

Moisture held in the cell cavities (lumens) of wood, not chemically bound to cell walls. Free water is removed first during drying and does not cause shrinkage.

A longitudinal crack in a tree trunk caused by rapid temperature drop, creating tension in the outer wood layers. Common in hardwoods in cold climates.

Forest Stewardship Council certification — an independent third-party label verifying that forest products come from sustainably managed forests meeting environmental and social standards.

The G-layer (gelatinous layer) is a special cellulose-rich layer found in tension wood fibres in many hardwoods. It changes the way the cell wall behaves and is associated with elevated longitudinal shrinkage and distortion in boards containing tension wood.

The ability of wood to form strong adhesive bonds. Affected by moisture content, extractive content, surface porosity, and machining quality.

The systematic classification of lumber quality based on the percentage of clear-face cuttings obtainable from each board. Governed by NHLA rules for hardwoods.

The orientation and visible pattern of wood cells and fibres in a piece of timber. It describes both direction (how fibres run) and appearance (the grain pattern you see).

Concentric bands in a tree trunk visible on end grain, typically representing seasonal growth cycles (often annual).

Growth stress is internal stress that develops in a living tree as wood forms and the stem supports itself. When logs are sawn, growth stresses can be released, causing boards to spring, bow, or move even if moisture content is uniform.

Growth stresses are internal stresses that develop in a living tree as it grows and supports itself. When a log is sawn, these stresses can be released unevenly, contributing to warp, spring, and distortion even before drying stresses are involved.

A tubular channel within wood that produces and transports gum or resin. Present in some hardwoods like those of the Proteaceae and Myrtaceae families.

A localised accumulation of gum or resin within the wood, often appearing as dark, soft patches. Common in cherry, walnut, and some eucalyptus species.

A narrow channel through wood filled with accumulated gum or resin, often appearing as a dark line. Common in cherry, eucalyptus, and some tropical hardwoods.

A final finishing technique using a cabinet scraper hand tool to remove tearout and achieve a glass-smooth surface before applying finish.

A dense engineered panel made from exploded wood fibres, created by steaming and pressing under extreme pressure. Smooth on one side, textured on the other.

The inner, older wood in a tree that no longer transports water. It is usually darker and often more naturally durable due to extractives.

Thermal modification of wood at 180-230°C in a low-oxygen environment to permanently alter its properties. Reduces moisture absorption, increases dimensional stability and decay resistance, and darkens the wood.

Spiral ridges on the inner surface of tracheid cell walls, visible under magnification. Diagnostic feature in species identification.

A group of carbohydrates in plant cell walls that bind with cellulose and help form the matrix of the wood cell wall.

An internal drying defect characterised by cracks inside the timber that are not visible on the surface. Caused by drying too rapidly before moisture can migrate from the core. Often undetected until the board is sawn or planed.

Internal cracking that creates a honeycomb-like pattern of voids within the wood, caused by excessive drying stress before the moisture gradient has equalised.

A hygrometer is a device that measures relative humidity (and often temperature). In woodworking it’s used to understand the environment’s EMC range and anticipate moisture content changes and seasonal movement.

The ability of wood to absorb sudden energy loads without fracturing. High impact resistance is critical for tool handles, sporting goods, and flooring.

A foreign material or abnormal tissue trapped within the wood structure, such as bark, mineral deposits, or insect debris.

Tubular passages in wood that carry resin or gum, surrounded by specialised secretory cells. Characteristic of species like pine, spruce, and some tropical hardwoods.

Grain where the fibre direction alternates (often in bands) so that it reverses direction repeatedly through the wood.

A standard test of wood hardness that measures the force required to press a steel ball into wood to half the ball’s diameter.

Creating a perfectly straight, flat reference edge on a board using a jointer or hand plane. The jointed edge serves as the baseline for subsequent ripping and surfacing operations.

Kerf is the width of material removed by a saw cut—the thickness of the slot left behind. Kerf affects yield (waste), cutting power, and surface quality; thinner-kerf blades generally waste less wood.

The controlled process of removing moisture from timber using heat and airflow in a chamber. Kiln drying accelerates the natural seasoning process, reducing moisture content to a target level (typically 6-8% for furniture, 12-18% for construction) in days rather than months.

A joint where two overlapping pieces of wood are joined together. One of the simplest wood joints, suitable for framing and box construction.

Wood formed later in the growing season when growth slows, typically darker and denser (with smaller cells and thicker walls).

A complex polymer in wood cell walls that acts like a natural adhesive, binding cells and giving wood rigidity and compression strength.

The direction along the grain, parallel to the tree trunk axis. Most wood strength and stiffness is greatest in this direction.

Longitudinal shrinkage is the change in length of wood as moisture content changes below fibre saturation point. In normal mature wood it is usually very small (~0.1–0.3% from green to oven-dry), but it can be much higher in juvenile wood and reaction wood.

A woodworking tool consisting of a beam with a marking pin or knife that scribes lines parallel to a reference edge at a set distance.

Medium density fibreboard — an engineered panel made from wood fibres bonded with resin under heat and pressure. Uniform density and smooth surface, widely used for painted cabinetry.

Bands of cells that run radially from the centre of the tree toward the bark, used by the living tree for storage and transport across the trunk.

A microclimate is a local zone where temperature and humidity differ from the surrounding space (e.g., near radiators, exterior walls, inside cabinets). In woodwork, microclimates can cause uneven moisture exchange and lead to cupping or distortion.

Microfibril angle (MFA) is the angle between cellulose microfibrils in the S2 layer of the cell wall and the cell’s long axis. Lower MFA generally increases stiffness and keeps longitudinal shrinkage low; higher MFA (common in juvenile and reaction wood) increases longitudinal shrinkage and distortion risk.

Dark discoloured bands running along the grain, formed by chemical deposits (often iron) accumulated in the tree. Common in walnut and oak.

Lumber sold with a range of board lengths in a bundle rather than sorted to a single length. Common for lower-grade hardwood lumber.

A measure of wood stiffness — the ratio of stress to strain under bending load. Indicates how much a board will deflect under load. Also called MOE.

The amount of water in wood expressed as a percentage of the oven-dry wood mass.

A moisture gradient is a difference in moisture content between the surface and the core (or between faces) of a piece of wood. Gradients create internal stress during drying and can cause distortion when material is removed or conditions change quickly.

A woodworking joint where a protruding tenon on one piece fits into a matching mortise (slot) on another. One of the strongest and oldest wood joints, used in framing and furniture.

The degree to which wood expands and contracts with changes in moisture content. Tangential shrinkage is typically 1.5-2x radial shrinkage, causing significant movement in flat-sawn boards.

The ease of driving nails into wood and their holding power once set. Determined by density and fibre structure. Dense hardwoods resist nailing but provide strong holding power.

Second-grade NHLA hardwood lumber with minimum clear-face yield of 66-2/3%. Suitable for furniture components and smaller parts.

A lower grade in the NHLA grading system with minimum clear-face yield of 50%. Suitable for furniture and cabinetry parts that are 3 inches or smaller.

A wood texture where pores/vessels are large and prominent, leaving visible open pores on the surface (often requiring grain filling for a glass-smooth finish).

A general term for living wood cells that store and transport nutrients (in rays and axial bands). In timber, parenchyma can appear as light streaks or bands.

An engineered wood panel made from wood chips, sawmill shavings, or sawdust bonded with synthetic resin and pressed. Cheaper than MDF but less dense.

Programme for the Endorsement of Forest Certification — an umbrella organisation promoting sustainable forest management through independent third-party certification. The world's largest forest certification system.

The specialised end walls between vessel elements in wood, with openings (perforations) that allow water flow between adjacent cells. Type varies by species.

The degree to which fluids and gases can pass through wood. Affects drying rate, treatability with preservatives, and movement of moisture during service.

Living tissue in a tree that transports sugars and other products of photosynthesis from leaves to the rest of the plant.

The organised stacking of lumber for seasoning or storage, ensuring proper sticker placement, weight distribution, and protection from ground moisture.

Very small knots (less than 6mm diameter) typically from small branch growth. Common in species like cherry and maple. Considered attractive in furniture grade rather than a defect.

The small central core of a tree stem around which the first growth formed. It is typically less stable and often associated with cracking and distortion when included in boards.

The arrangement of pits (thin areas in cell walls) that allow communication between adjacent cells. Inter-vessel pitting patterns are important for microscopy-based identification.

Plain-sawn (also called flat-sawn) describes boards cut tangentially to the growth rings so the rings meet the face at a low angle (often ~0–30°). It maximises yield and width, often shows “cathedral” grain, and is generally more prone to cupping than quarter-sawn stock.

Lumber (usually British terminology) that has been planed on all four faces to a smooth finish. Equivalent to S4S in North America.

The process of smoothing a wood surface with a plane or planer, creating a flat, dimensioned board. Essential for achieving precise joint fit and finish.

An engineered wood panel made by gluing together thin sheets (veneer) of wood with alternating grain direction. The cross-lamination creates uniform strength in all directions.

A woodland management practice similar to coppicing but performed higher up the trunk, above browse height. Allows regrowth while protecting new shoots from grazing animals.

A process where chemical preservatives are forced deep into wood fibres under high pressure, significantly extending the service life of timber exposed to decay, insects, and moisture. Common for outdoor decking, fencing, and structural applications.

Boards cut so the growth rings are closer to perpendicular to the wide face (typically 60–90° ring angle), exposing more radial grain.

A rectangular recess cut into the edge of a board, creating a step or L-shaped profile. Used in cabinet joinery and case construction.

Direction from the pith outward to the bark, crossing growth rings at right angles. One of the main axes used to describe wood movement and properties.

A condition where the hard latewood stands above the softer earlywood after planing, creating a textured surface caused by dull tools or high moisture content.

Ray fleck is the shimmering or ‘flake’ figure seen on the face of some quarter-sawn hardwoods (especially oak), caused by large medullary rays being cut and exposed. It’s a visual indicator of a radial surface and is often associated with improved stability.

Horizontal wood tissue extending radially from the pith toward the bark, responsible for lateral transport and storage of nutrients. Visible as flecks and rays in quarter-sawn timber.

Radial sheets or ribbons of cells running from the centre of the tree outward. On end grain they appear as fine radial lines, and on quarter-sawn faces they can produce ray fleck figure.

Wood with abnormal structure formed by a leaning or stressed tree to correct its posture. It can have unusual shrinkage and internal stress behaviour.

A kiln process applied after drying to relieve internal stresses and case hardening by reintroducing some moisture through steaming or controlled humidity.

The replanting of trees on land where forests have been cut down or destroyed, restoring forest cover and ecological function.

The process of renewing a forest stand through natural seeding, planting, or artificial means. Essential for sustainable forest management.

Relative humidity (RH) is the percentage of water vapour in the air compared with the maximum the air could hold at the same temperature. RH strongly controls wood’s equilibrium moisture content (EMC), and therefore moisture content and movement.

Specialised tubular channels in some softwoods (and a few hardwoods) that contain and transport resin (oleoresin).

A specialised tubular structure in softwoods (conifers) that produces and stores resin. Normal resin ducts are anatomically consistent; traumatic resin ducts form in response to injury.

Parenchyma cells arranged in a net-like or reticulated pattern, forming an interconnected system within the wood structure.

Alternating bands of light and dark caused by cutting interlocked grain on a quarter, revealing the alternating grain direction as parallel stripes.

Boards cut so the growth rings meet the face at roughly 30–60° (often aiming near 45°), producing very straight, uniform grain.

Complete separation of adjacent growth rings, creating a gap in the wood. Weakens the board and creates potential failure points.

A hardwood where the pores (vessels) are much larger in earlywood and smaller in latewood, forming a distinct pore band each growth ring.

Cutting wood along the grain (parallel to the fibres), typically separating fibres and following the board’s length direction.

Advanced wood decay caused by wood-destroying fungi, classified as brown rot, white rot, or soft rot. Each type attacks different wood components (cellulose, lignin, or both).

Rough milling is the process of machining wood slightly oversize (in thickness/width) and then letting it rest so stresses can redistribute and moisture can equalise before final milling to finished dimensions.

Lumber that has been sawn to size but not been surfaced or planed, retaining the rough texture from the saw.

Machining decorative profiles, grooves, or shaped edges using a router with a cutting bit. Common for mouldings, dados, and custom edges.

The S2 layer is the thickest layer of the secondary wall in most wood cells. It contains most of the cell wall’s cellulose microfibrils and largely controls stiffness and shrinkage behaviour, including the effect of microfibril angle on longitudinal movement.

Surfaced Two Sides — lumber that has been planed on the two broad faces but left rough on the edges.

Surfaced Four Sides — lumber that has been planed flat on all four faces, dimensioned to consistent thickness and width.

Surface finishing using abrasive paper to smooth wood, removing tool marks and preparing the surface for finish application.

The outer, younger wood in a tree that actively transports water and nutrients when the tree is alive.

A specific type of vessel end wall perforation pattern in wood, with horizontal bars resembling ladder rungs. Important for microscopic species identification.

The process of drying green (fresh-cut) timber to reduce its moisture content to a level appropriate for its intended use. Proper seasoning prevents warping, cracking, and structural failure.

A harvesting method where only selected mature trees are cut, leaving the rest of the stand to regenerate naturally. More ecologically sustainable than clear felling.

NHLA grade for softwood lumber, appearance-graded for finish quality. The best face is nearly free of defects, suitable for painting or staining.

A separation between growth rings, usually caused by failure along the ring boundary (often from growth stress, frost, or mechanical damage).

The ability of wood to resist forces that cause sliding failure along the grain. Important for joints, fasteners, and load-bearing connections.

A precision jig used with a hand plane to accurately trim board edges to exact angles (90° or custom bevels) in repeatable fashion.

A shrinkage coefficient is a factor used to estimate how much wood will change dimension for a given change in moisture content, in a specific direction (tangential, radial, or longitudinal). Coefficients vary by species and are used in movement calculations (ΔW).

The proportional reduction in timber dimensions from green to oven-dry state. Expressed as percentage loss in tangential, radial, and longitudinal directions.

The art and science of controlling the establishment, growth, composition, health, and quality of forests to meet diverse needs and values.

Dark lines formed in wood by fungi as they grow along grain boundaries. The contrasting patterns are highly valued in decorative woodwork. Common in maple, sycamore, and birch.

The ratio of the density of wood to the density of water, measured at oven-dry weight. Used to compare wood density across species and predict weight, strength, and shrinkage.

Grain where fibres spiral around the tree trunk axis rather than running straight, leading to boards that may twist as they dry or are machined.

A separation of wood fibres extending from the surface inward, typically caused by drying stresses or mechanical impact. Reduces structural integrity and usable area.

A longitudinal curvature of timber along its length, causing it not to lie flat. Sometimes used interchangeably with bow, though spring can specifically refer to twist-induced curvature.

The proper arrangement of timber in a pile with stickers for seasoning. Correct stacking ensures even air flow and prevents warping and decay.

Radial cracks extending inward from the bark toward the pith in a star-like pattern, caused by rapid drying or extreme frost during tree growth.

A wood treatment process that applies steam to timber at high temperatures, often used to darken colour (as in American black cherry), relax internal stresses from kiln drying, and improve dimensional stability.

A narrow strip (usually wood) placed between layers of boards during air drying to create air gaps and allow moisture to escape evenly. Also called spacer.

A surface crack caused by intense solar heating of one side of the tree trunk, leading to uneven expansion and contraction of the wood.

Surface checking is cracking on a board’s surface caused by excessive tensile stress in the drying shell when the surface shrinks before the core. It’s a common drying defect in dense species and thick stock when early drying is too aggressive.

The T/R ratio is the tangential-to-radial shrinkage ratio for a species. It compares how much wood shrinks tangentially (along the growth-ring curve) versus radially (across the rings). A higher T/R ratio generally means flat-sawn boards are more likely to cup and show uneven movement compared with quarter-sawn boards.

Direction tangent to the growth rings (along the curve of the rings). It is typically the direction of greatest shrinkage and swelling in wood.

A rough, torn surface created during planing, routing, or machining when fibres are lifted and broken out instead of being cleanly cut.

The projecting tongue or extension cut on the end of a wood member that fits into a matching mortise to form a joint.

Tension wood is reaction wood formed in hardwoods on the upper side of a leaning stem or branch. It often contains a G-layer and can cause abnormal longitudinal shrinkage, fuzziness when machined, and distortion during drying.

Through-and-through sawing is a plain-sawing variation where a log is sliced in one direction without turning it between cuts, producing a stack of boards with mixed ring orientations (more flat-sawn towards the outside, closer to quarter-sawn nearer the centre).

Raw sawn wood ready to be worked into finished products. Refers to inventory of lumber available for a project.

A joint where a protruding tongue on one board's edge fits into a matching groove on the adjacent board. Used in flooring, panelling, and panelling systems.

Long, slender cells found in softwoods that perform both support and water transport functions (softwoods largely lack vessels).

Treatability describes how easily a wood species (usually its sapwood, and sometimes its heartwood) can be impregnated with preservative treatments. Low-treatability woods resist chemical penetration, which affects how suitable they are for exterior use when relying on treatment rather than natural durability.

A precision measuring and marking tool with a fixed 90° angle between the blade and the stock, used for checking squareness and marking cross-grain lines.

A warping defect where the corners of a board lie in different planes, creating a spiral distortion along its length. Often caused by spiral grain in the standing tree or uneven drying.

Twisting is a type of warp where a board’s corners lift in different directions so the board becomes a ‘propeller’ shape. It often relates to spiral grain or uneven shrinkage and stress release during drying.

Axial parenchyma cells that surround wood vessels in a sheath-like arrangement. A diagnostic anatomical feature in many tropical hardwoods.

Thin sheets of wood (typically 0.6-1.5mm) sliced from a log and glued to a substrate to create a decorative surface with the figure of expensive wood at low cost.

Large tube-like cells in hardwoods that transport water in the living tree. On sawn timber they appear as pores in the grain.

The presence of bark, or lack of wood, on the edge or corner of a board. Common in boards cut near the outer perimeter of a log, reducing the usable cross-section.

A waney edge is a board edge that still has bark or the rounded outer surface of the log (wane), rather than a fully squared edge. It can reduce usable width and may be unacceptable in some grades, but can be a deliberate feature in “live edge” work.

A general term for any deviation from a flat or straight board surface. Includes bow, crook, cup, and twist — each describing a different geometric distortion of the timber.

A figure pattern where the grain direction varies along the length of the board in undulating waves, creating a rippled appearance on the surface.

The ability of wood to withstand surface abrasion and friction. Directly related to density and hardness. Important for flooring and high-traffic applications.

Wood movement is the predictable shrinking and swelling of wood as its moisture content changes below fibre saturation point. It happens mainly across the grain (tangential and radial) and is the reason solid-wood panels, tabletops, and joints must be designed to allow seasonal dimensional change.

A fuzzy, torn surface on machined wood caused by dull cutters, improper cutting angles, or machining wood with interlocked or irregular grain.

A species-specific assessment of how easily wood can be cut, shaped, and finished. Includes factors like hand tool response, machining quality, and gluing.