Adhesief : Adhesive

An adhesive is a substance used to stick two surfaces together.  

Examples of an adhesive substance are cement, gum, and various glues.


Beweging : Movement in wood

When a tree is first felled, it is considered to be in the green state, and contains a very large amount of moisture. The humidity is reduced by drying to approximately 12%. Wood being hygroscopic means that it, like a sponge gains or looses moisture from the air. It will also expand and contract in relation to this gain or loss of moisture. In other words swelling or shrinking. This we call movement.

Because the guitar builders involved in the Leonardo Guitar Research Project use mostly dried wood we shall only consider movement and the faults which are thereby caused.

Broosheid : BrittlenesspastedGraphic.png

Modulus of elasticity (MOE) testing

Technically it’s a measurement of the ratio of stress placed upon the wood compared to the strain (deformation) that the wood exhibits along its length. MOE is expressed in pounds-force per square inch (lbf/in2) or gigapaschals (GPa). This number is given for wood that has been dried to a 12% moisture content, unless otherwise noted. (source:

Practically speaking, brittle wood splits and breaks with little effort, when twisted is easily breaks apart. It has very little flexibility.

Sugar Maple is a heavy wood type with it’s 720 kg/m3 in which we assume great strength. However this is a brittle wood. We often see wood with a large density are rarely flexible and depend on their strong fibres, after a heavy impact, to return to their original shape. So while sometimes very elastic they remain very stiff. Such wood types, show after heavy impact, microscopic cracks and eventually break without warning.

Take note that while elasticity and stiffness are not contradictory to each other they are also not always comparable.

Buigbaarheid onder impact : Impact Bending

The measurement of applying resistance to sudden loads: Also the capacity to absorb energy. The malleability is measured by subjecting a piece of wood to sudden impact by a weight being dropped on it. The height the fall determines the amount of flexibility during impact. The test of flexibility under a short impact is characterised by it’s short duration. Flexibility is important in guitar building unless the guitarist is planning to smash the guitar to bits after the concert.

Buigen : Bending

By placing pressure perpendicular to the longitudinal axis of the wood. A small radius produces a sharp curve and a large radius a produces a soft curve.

Whatever method we use, be that cold, during or after steaming, by use of a bending iron or clamps we identify the following:

* Easy to bend wood. Wood which does not break and holds it’s shape after bending, be that a small or large radius. The wood does not twist or loose it’s colour permanently. 

  • Care needed when bending due to specific characteristics such as; the wood discolours easily due to extraction residues. It returns easily to original shape which necessitates clamping for a period of time. Extra precaution is necessary when bending to a small radius but it doesn’t break and it doesn’t twist anymore than other wood sorts.

  • Wood which is difficult to bend, breaks easily during bending or shows such and elasticity that it returns to it’s original shape even after bending. A possibility that the wood deforms due to internal stress or perhaps due to the direction the wood has been sawn.


*Wood which breaks immediately due to it’s brittleness and       is therefore impossible to bend

Buigsterkte : Bending strength 

Or ‘modulus of rupture’ or ‘maximum bending stress’ is the extent to which a material can bend while placed under extreme pressure on it’s long axis, without breaking and without extending beyond it’s elastic limit. The Modulus of rupture is measured during a static bending test whereby the pressure is slowly increased. Just as with the modulus of elasticity the results are expressed in N/mm2.


Cambium : Cambium

The vascular cambium (also called main cambium, wood cambium, bifacial cambium; plural cambia) is a plant tissue located between the xylem and the phloem in the stem of a vascular plant. It is a cylinder of unspecialised meristem cells that divide to form secondary vascular tissues. Namely, it is the source of both secondary xylem growth inwards towards the pith,and secondary phloem growth outwards to the bark.    

(source wikipedia)


Defecten door beweging : Defects due to movement

The dimensional changes that accompany the shrinking and swelling of wood are major sources of both visual and structural problems in guitar making. Shrinking and swelling occur as the wood changes moisture content in response to daily as well as seasonal changes in the relative humidity of the atmosphere, i.e., when the air is humid, wood absorbs moisture and swells; when the air is dry, wood loses moisture and shrinks. When this occurs on different axes and at different rates, the result is deforming of the wood.

The four most common deformations :

  • Bow
  • Crooked
  • Twist
  • Hollow

Place drawings and photos from website here please …!!!!

Densiteit : Density 

Density; or volumetric mass density ;  is the unit weight express as (lb/ft3), (gm/cm3) or (kg/m3).

This expresses how much one cubic foot, one cubic centimetre or one cubic meter of wood weighs.  The weight varies according to the moisture content of the wood. The density is measured when the wood has been oven dried to a moisture content of 12% or less. The density is used to form an idea of the hardness or softness of the wood.

  • Lightly dense wood such as European Den (Picea abies) White Poplar (Populus alba) are examples of wood with a density of 400 and 440 kg/m3.
  • Middle dense wood varies between 500 kg/m3 to 700 kg/m3. European Maple ( Acer Pseudoplatanus L.) has a density of 600 kg/3m. 
  • Dense wood is heavy wood and is often hard wood with a density between 7àà to 1355 kg/m3. Ebony has for example a density of approximately 960 - 1120 kg/m3. Beech (fagus sylvatica) dried weighs 710 kg/m3.

Dichtheid : Density 

See Density:

Dosse : Plain sawn


The type of wood cut is determined by the angle at which a board is cut from the log. There are three cuts of wood:  Plain sawn (AKA Flat sawn), Quarter sawn, and Rift Sawn and each cut produces a board of a different appearance and quality.


Plain Sawn: The most common cut is plain sawn. The log is squared and sawed lengthwise in a series of parallel cuts. The annual growth rings appear as approximately straight lines on the board, joining at the end to form a “cathedral arch.” Because of this arch, plain sawn boards are often considered the most beautiful of the cuts. These boards are ideal for large visual areas like whole floors, tabletops, drawer fronts, sides of dressers or other similar projects. Plain sawn boards are the least expensive of the three cuts as they are the least labor-intensive to produce and leave the least waste.

Draad : Grain


R. Bruce Hoadley wrote that grain is a "...confusingly versatile term..." including the direction of the wood cells (straight grain, spiral grain), surface appearance or figure, growth-ring placement (vertical grain), plane of the cut (end grain, quarter sawn, flat sawn, etc.), rate of growth (narrow grain), relative cell size (open grain), and other meanings.

Physical aspects

Perhaps most important physical aspect of wood grain in woodworking is the grain direction or slope (e.g. against the grain). The two basic categories of grain are straight and cross grain. Straight grain runs parallel to the longitudinal axis of the piece. Cross grain deviates from the longitudinal axis in two ways, spiral grain or diagonal grain. The amount of deviation is called the slope of the grain.

In describing the application of a woodworking technique to a given piece of wood, the direction of the technique may be:

with the grain (easy; giving a clean result)

against the grain (heavy going; giving a poor result such as chipping or tear-out)

across the grain (direction of cut is across the grain lines, but the plane of the cut is still aligned with them)

end grain (at right angles to the grain, for example trimming the end of a plank)

Grain alignment must be considered when joining pieces of wood, or designing wooden structures. For example, a stressed span is less likely to fail if tension is applied along the grain, rather than across the grain. Grain direction will also affect the type of warping seen in the finished item.

In describing the alignment of the wood in the tree a distinction may be made. Basic grain descriptions and types include:

straight - grain which runs in a single direction, parallel to the axis of the tree

spiral - grain which spirals around the axis of the tree

interlocked - grain which spirals around the axis of the tree, but reverses its direction for periods of years resulting in alternating directions of the spiral grain.


Sketch of A—Quarter-sawn & B—flat-sawn

typically figured red gum table

mountain ash floor, showing some fiddleback figure (source wikipedia)


Elasticiteit : Elasticity  (Refer to Young’s modulus of elasticity)

When an external pressure is exercised upon a material it returns to it’s original shop when that pressure is released. Almost all materials are have some elasticity. By gradual implementation of a force upon a material, at some point a limit will be reached, whereby the material can no longer return to it’s original shape or form. This is the elastic limit of the material. Each bit of pressure beyond this limit is then called ‘permanent position’.

Elasticity is expressed in N/mm2, and determines the stiffness of the material and not it’s strength. Take of example a hockey stick. This could be made out of material that doesn’t break easily but has little elasticity. At the first impact the stick wouldn’t break but would bend and remain bent. This we want to avoid with hockey sticks. Therefore hockey sticks are made out of ash (Fraxinus excelsior). Moreover ash has the capacity to absorb sudden shocks. On the other hand, as guitar builders we choose a wood that bends well and holds it new shape.

See also: Stiffness, bending strength, bending under impact and wood strength.

Extractie resten : Extraction residue 

Other than the most important substances in wood such as cellulose, hemicellulose and lignin will be known as extraction residues. Examples are, resin, oil and turpentine wax.

These extraction residues offer the trees a natural protection against insects and fungi.

These extraction materials can have a blunting effect on cutting tools. They can also lead to difficulties in the drying of the wood making it almost impossible to impregnate.


Golvende draad : Wavy grain 

There is such a thing as wavy grain which does not run parallel with the core of the tree. A wavy surface will result from splitting this wood tangentially. finishing this wood will deliver a stripy effect (Moiré effect) which is sought after by luthiers. A good example of this is maple (Acer pseudoplatanus L.)

Groeiring : Growth ring

growth ring also know as year ring : see ‘growth zone’

Groeizone : Growth zone

The growth ring  also called the annual or yearly rings are the layers of wood produced by a single year's growth of a woody plant. In some woods these can be identified by one dark and one light ring. Summer (early) and winter (late) growth.


Hardhout : Hard wood

Hard wood (different from hardwood) is wood with a high density and/or specific gravity

.European beech (Fagus sylvatica) and ebony (Diospyros

.Specific gravity is about 0.6 - 1.2

.Density varies from 700 kg/m3 to 1355 kg/m3

Note: The definition that we use here is not directly related to the Lanka hardness test. This test is based on a specific interpretation of the concept of hardness whereby this indication of hardness is less useful within the musical instrument construction.

Hardwood : Hardwood

(hardwood; angiosperm trees; broadleaf trees)

The term hardwood has nothing to do with the strength or hardness of the wood but with the cell structure.

Harthout : Pith

(Pith, not to be confused with ‘heartwood’) is the middle of the tree trunk. The first growth ring, mostly unusable.

Houtvat : Vessel 

Wood vessel consists of pores which are relatively large in diameter, but have thin walls.This houtvatelementen form long end-to-end series in the tree.At the end of their development phase tusse the walls disappear completely. They form long tubes or pipes. Depending on the wood for , they can be 6 to 8 meters long.These pores differ in diameter and distance from each other and together with other elements define the texture of the wood. Pore frequency is generally only measured on diffuse-porous woods; if noted, it’s indicated in comparative terms, such as few, or numerous, rather than by precise microscopic terms such as quantity per square millimeter.

.      < 25 Mu)  = extremely narrow     ex. nexus (Buxus sempervirens).

.     25-50 Mu  =  very narrow             ex. Willow (Salix spp.)

.   50-100 Mu  =  narrow                     ex. Maple (Acer spp.)

. 100-200 Mu  =   average                  ex. Goupia glabra.

. 200-300 Mu  =  wide                        ex. Azobé (Lophira alata)

. 300-400 Mu  =  very wide                ex. Essessang (Ricinidendron)

.     > 400 Mu  =  exceptionally wide  ex. Pangapanga (Millettia stuhlmanii)

Sources of reference: Understanding Wood ,a Craftsman’s Guide to Wood Technology by R.Bruce Hoadley   


The wood sample on the left is Brazilian Rosewood (Dalbergia nigra), which has very few pores. The sample in the middle is East Indian Rosewood (Dalbergia latifolia), a close relative which is frequently confused with Brazilian Rosewood; its pores are about twice as numerous as the Brazilian sample. 

The sample on the right is European Ash (Fraxinus exselsior).

Houtvezels : Wood fibres

Wood fibres; cellulose fibres.

Wood fibers are elongated, horizontal axial cells which provide for the strength and stiffness of the plant.

Cellulose is a very important polysaccharide because it is the most abundant organic compound on earth. Cellulose is a major component of tough cell walls that surround plant cells, and is what makes plant stems, leaves, and branches so strong.

The presence of a lot of wood fibres (such as, for example, in late wood and 95% in conifers) indicates strong  'lignification' of the timber.


Remark: Houtvezels (wood fibres) are not in English 'vessels', the latter are in fact  ‘xylem’.Xylem is one of the two types of transport tissue in vascular plants, phloem being the other. The basic function of xylem is to transport water from roots to shoots and leaves, but it also transports some nutrients.[1] The word xylem is derived from the Greek word ξύλον (xylon), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant.(Wikipedia)




Jaarring : Spinthout : Growth zone 

(See growth zone)

Janka Hardheidtest : Janka hardness test

The hardness of a wood is rated on an industry wide standard known as the Janka test. The Janka test measures the force required to embed a .444 inch (11,287 mm) steel ball into the wood by half its diameter.  This test is one of the best measures of the ability of a wood specie to withstand denting and wear.

For more information see : US Department of Agriculture (USDS), The Encyclopedia of Wood, Skyhorse Publishing Inc. 2007 (Kindle ref:2593)

Jeugdhout : Sapwood 

Sapwood is the living, outermost portion of a woody stem or branch, while heartwood is the dead, inner wood, which often comprises the majority of a stem’s cross-section. You can usually distinguish sapwood from heartwood by its lighter colour.

But, colour in wood can be very misleading; not all heartwood is dark and not all dark-coloured wood is heartwood. And, the relative amounts of sapwood and heartwood in any stem can vary greatly among individuals, species, and growing conditions. So, for a more accurate – and less specious – distinction, we need a more complete understanding of what wood is and how both sapwood and heartwood form. This won’t hurt.

All wood starts as sapwood. It is formed just under the bark by a thin layer of living cells known as the cambium, which produces bark cells to the outside and wood cells to the inside. Tree stems increase in girth during each year of growth because a new layer of wood cells is added inside the cambium. In good growing years, this new layer of wood can be many cells thick, and in poor years, it is relatively thin. Regardless of thickness, when any such growth occurs, the cambium moves outward to accommodate the new layers of wood forming inside. Sapwood – this newly formed, outermost region of wood – contains a variety of cell types, most of which are living and physiologically active. This sapwood is where water and dissolved minerals are transported between the roots and the crown of the tree and, to a lesser extent, where energy reserves are stored.

In young trees and young parts of older trees, all of the wood in the stem is sapwood. But as the tree gets older and its trunk increases in diameter, things change. No longer is the entire cross-section of the trunk needed for conducting sap. This, combined with an increased need for structural support, causes significant changes in the wood. The cells nearest the centre of the trunk die, but they remain mostly intact. As these older sapwood cells age and die, they become heartwood. That is, they are altered to accommodate a shift in function. As residues of the once-living cells and additional chemical compounds from elsewhere in the plant accumulate in the heartwood, those cells cease to transport water or store energy reserves.

These compounds (including resins, phenols, and terpenes, sometimes referred to as extractives) not only help make heartwood more resistant to attack by insects and decay organisms but also tend to give this inner portion of the stem a distinctive darker colour. For example, the famous dark brown of black walnut lumber and the striking red hues of black cherry boards occur only in the heartwoods of these trees, and both owe their characteristic colours to these chemicals.

Such woods are highly prized largely because of their coloured heartwoods, but it is important to remember that colour alone is not the sole distinction between sapwood and heartwood, regardless of species. Indeed, wood can be coloured for reasons unrelated to heartwood. There are many discolourations associated with injury or fungal infection of wood, for example, and some heartwoods – including that in most spruces, fir, cottonwood, and basswood – are naturally very light coloured. Then again, if these light-coloured heartwoods are injured, they often do become darkened by discolouration. So, in summary, sapwood, which is nearly always light coloured, results from new wood formation. Heartwood, which is often – but not always – dark coloured, results from the natural aging process of the tree. But both can be discoloured by many other causes.

Typically there is less sapwood than heartwood in any given stem. The exception, of course, is in young trees and the youngest portions of stems and branches on older trees which – because they are young – are naturally dominated by sapwood. The proportion of heartwood to sapwood in the main stem does vary with species. Black locust, for example, usually has a very narrow band – often less than an inch – of functioning sapwood, whereas maple stems often can have many inches of sapwood and relatively narrow cores of heartwood. In general, more vigorously growing trees tend to have wider bands of sapwood.

This sapwood-heartwood distinction has important implications for woodworkers beyond the obvious implications of colour. Because sapwood contains the sap-conducting cells of the tree, it tends to have a relatively high moisture content. This is good for the living tree but it is not so good for the woodworker, because sapwood tends to shrink and move considerably when dried, and it is much more susceptible to decay and staining by fungi.

(Source: )


Juvenile hout : Juvenile wood

The first five to fifteen rings surrounding the kern or pith of the tree are known as juvenile wood and is generally of poor quality. Remark: Not to be confused with sapwood.


Kernhout : Heartwood

Heartwood or "duramen 'is the innermost portion of a trunk that corresponds to the oldest growth rings formed (without the marrow), and that does not contain live cells. The nutrients have disappeared from this timber and converted into other substances. Because of this, and due to the presence of extraction residues, this wood is less prone to be attacked by insects and fungi.The heartwood is generally harder, drier wood with greater density and often darker than the outer layers of wood.

Kleur van kernhout : Colour of heartwood.

The colour of heartwood can vary enormously even within the same plank. The colour is influenced by various things. For example by different elements deposited within the pores, influence by UV light while growing. And of course there is quite often, but not always, a difference in colour between the sapwood and the heartwood. We notice less of a difference between sapwood and heartwood in trees which grow in a temperate climate than those which grow in a tropical climate. 

We onderschieden: We differentiate.

Rijphoutboom : Ripewood

The more or less indistinct inner wood of some species, in which the sapwood has aged and presumably died with little if any deposition of the substances associated with heartwood.


                 Beech (Fagus sylvatica) and Lime (Tilia europaea). Beech can, on occasion, show a darkening of the centre because of insufficient antibodies being produced (against bacteria and fungi) in the heartwood and is therefore only as durable as the sapwood.  

Spinthoutbomen : Sapwood

In sapwood trees there is little or no distinction between the heartwood and the outer sapwood. The heartwood continues to function in the same way as the sapwood. This not only makes it difficult to see a colour difference but also makes the heartwood as susceptible to threat from sickness and fungi as the sapwood.


                 Poplar (Populus alba) and Birch (Betula pendula)

Kops : End grain  

A saw cut perpendicular to the grain, right through the longitudinal axis through the rings provides a front face with more or less crosscut. We choose to speak of the 'transverse plane' (x). In this area we have a nice overview of the annual rings. End grain.

Krimp : Shrinkage versus swelling

When green wood dries, the unbound water first evaporates from the cells to a humidity of about 28%. Beyond 28% the bound water evaporates from the cell walls causing shrinkage in the wood. Mainly in a direction at right angles to the longitudinal axis (or at right angles to the longitudinal axis of the wood cells)

Shrinkage continues until the moisture content of the wood in an equilibrium comes with the humidity of a certain place and a certain time of year. In our regions this means that wood stored outdoors will reach a humidity of 12 to 15%. Conversely, the wood will swell up again with water when it is exposed to a higher than normal humidity. The wood is dried for processing in order to counteract the unwanted effects caused by shrinkage. The greatest loss of water takes place during this initial contraction phase, thereby revealing any major defects in the wood.


Krimpen en Zwellen :Interlocked grain

The grain goes alternately helically around the tree. For example during one growth season it may grow clockwise and the ext season anticlockwise. This occurs very regularly. There are few European woods with interlocked grain, this is more common in tropical wood types. Interlocked grain is clearly visible on the radial plane. Bumps and wells are often caused in the wood by the interlocked grain and become visible when working the wood. For example, while planing and scraping. The wells are caused by torn out wood fibres. A lot of distortion can happen during the drying process.

Kwartiers: Radial cut wood: radial grain: quarter grain.


A saw cut parallel to the wood fibre and parallel to the central axis of the trunk, in the direction of the radiant, through the heart of the tree, results in a radial plane with more or less quarter cut timber.

Both the radial axis (R) and the longitudinal axis (L) deliver this quarter cut timber. We choose "radial axis (R) rather than a quarter sawn. See also ‘Three Axis’ and ‘Saw direction’.


Laathout : Late wood or Summer wood

Licht Host : Light wood 

° Examples of light wood:  white poplar (Populus alba) and white           willow (Salix alba).

° Specific gravity around 0.15 - 0.45

° Density varies from 300kg/m3 to 500kg/m3 (see specific gravity)

Lijmen : Bonding

Bonding is sticking materials together by means of some kind of adhesive.


° Wood which is easy glue: the wood easily soaks up water and     enough glue remains on the surface to ensure a good bonding.

° Wood which need preparation:For example end grain soaks too much up and needs to be sealed with extra layers of glue before final glueing.

° Wood which is difficult to glue: Due to the extreme density of the wood the water (glue) remains on the surface and doe not soak in. Also wood with an oily surface or covered with natural residue (resins etc.). It should also be noted that wood that has been sawn with a blunt blade leaves a shiny surface which also can impair bonding.


Merg : Pith

Also called heartwood is the the first annual ring right in the middle of the tree trunk. This wood often unusable. 

(See also structure of wood trunk)


Nerf : Grain

(In the sense of ‘Relative pore size’; we’ll use texture)

(See texture)


Orthotropische aard van hout : Orthotropic nature of wood

Wood has unique and independent of each other properties depending on the direction (on 3 axes) in which the timber is located in the trunk. Therefore  the sawing direction is a relevant parameter for the determination of the process ability (usability) of wood.


Porie : Pore

(A cross section of a pore is a vessel).

 If the wood is sawn perpendicular to the axis of the trunk, we see through a lens of x10 the diameter of the pores and their distribution

(closed, open or far apart).  

Because all hardwood has timber vessels, we call hardwood  a porous wood. Pores in hardwood, along with the grain tell us  something  about the texture of the wood. The texture determines the smoothness of the timber surface.

° Examples of light wood:  white poplar (Populus alba) and white           willow (Salix alba).

° Specific gravity around 0.15 - 0.45

° Density varies from 300kg/m3 to 500kg/m3 



Radial as : Radial axis.

One of the three axes in a trunk.

The radial axis perpendicular to the wood fibres, through the growth rings in the direction of the rays. - > A saw cut in this direction runs across the grain. This reveals end grain.

Reactiehout : Reaction wood; compression wood & tension wood.

Reaction wood is abnormally shaped wood tissue that is associated with curved stems and branches of both softwood and hardwood. It occurs when the tree takes a more natural shape under the influence of the weather (wind, rain, snow ...) or in response to other factors (light, between other vegetation and rocks ...); hence the name "reaction wood”

° In Conifers is generally present in the fork of the branch  and in the inside bend of a curved trunk, and is called pressure timber. It is also recognisable by dark wood due to more winter growth.It can also be more opaque.

° In deciduous trees we find this abnormal tissue in upswept branches and sometimes in a middle section. It is called tension wood.Some tree species develop more tension wood than others. The fibres feel harder and form a fuzzy surface that is difficult to work with.

Reaction wood is wood under tension. This means that, more than in other woods, deformation will take place during the drying process. More so when the lumber consists of both tension wood and normal wood.  The shrink in longitudinal direction can be ten times more in reaction wood than normal wood.

Rechte draad : Straight grain.

The cells are more or less parallel to the longitudinal axis of the tree; this is an angle of less than 45 ° in the longitudinal cutting plane. 


Schaven : Planing

Planing is technique in which a strip (shaving) of material is removed, with a plane, in a cutting motion.


° Easy to plane wood: Ability to plane the wood neatly without tearing.The plane slides almost effortlessly leaving a smooth finish. The grain is straight.

° Where extra care is needed in setting up the plane. The wood is dense and it is necessary to wet the cutting blade often. More attention should be given to setting the cutting depth of the blade. The plane tends to glide more over the surface, instead of cutting, requiring more effort. The grain is mostly straight. By following the above requirements one quickly achieves a smooth finish.

° Difficult to plane wood : the grain of the timber prevents even and easy planing. To prevent wood tear-out the wood worker has to change planing direction from time to time. 

° Wood which is impossible to plane: The grain is as such that it is impossible to plane the wood. An alternative is to use a top router or sanding machine. Berchemia zeyheri. (Pink ivory)

Scheve draad : Twisted grain..?

On a radial plane straight grain can be seen. On the tangental plane we see grain that forms an angle greater than 45°.

Softwood : Conifer or gymnosperm trees.

Softwood is wood from gymnosperm trees such as conifers. The term is opposed to hardwood, which is the wood from angiosperm trees. The term ‘softwood’ has nothing to do with the strength of the tree but the cell formation.

Specifieke graviteit : Specific gravity 

by Eric Meier

In my experience, specific gravity is without a doubt the single most abused and vaguely used term in woodworking terminology.

Technically, specific gravity is a measure of the ratio of a wood’s density as compared to water. (So if a wood is of the same density as water, the specific gravity would be 1.00.) However, as with any density measurement for wood, it is greatly dependent upon the wood’s moisture content: the more moisture the wood contains, the denser it will be. The chief problem arises is that there is no standardised way between woodworkers and botanists to express specific gravity: and there is no implicit or assumed values. (At least with average dried weight, the moisture content is generally assumed to be at 12% unless otherwise noted.)

There are several ways to express specific gravity for wood—the standard within botany uses a wood’s oven-dry weight (meaning a moisture content of 0%, which is the lightest the wood can ever get), and its green volume, that is, when it’s freshly cut: having the largest possible volume. This may seem like a double-standard—to calculate this density from the wood’s dry weight, and its green volume—but this standardisation, commonly called the “basic specific gravity,” prevents any irregularities or inconsistencies from occurring, mainly because it uses predictable extremes (i.e., lightest weight and largest volume) to calculate the SG value. Such a combination is a real-world impossibility: it’s useful within the scientific community, but is very confusing for the woodworking community.

Other specific gravity values used in botany include using both oven-dry weight and volume, called oven-dry specific gravity. Another is to use the oven-dry weight, and the volume of the wood at 12% MC. The problem with these scientific measurements is that they use a non-existent ideal which never truly represents a given piece of wood at any one time. Since the weight is always based on the oven-dry value, it tends to produce an artificially low impression of specific gravity.

In addition to the variety of measurements used in botany, woodworkers also use various standards to gauge specific gravity—usually based on real-world wood samples. Accordingly, specific gravity measurements referenced in woodworking will usually be a pairing of green weight and green volume, 12% MC weight and 12% MC volume, and so forth.

Clear as Mud

Between scientific and woodworking standards, there are at least five different ways to express specific gravity, and oftentimes sources (particularly woodworking publications) will make no attempt at identifying which standard is being referenced. For instance, American Beech (Fagus grandifolia) could be as low as .54 for its basic specific gravity, or up to .73 for its specific gravity based on 12% MC weight and volume. (And if the wood were still green and above its fiber saturation point, its specific gravity could be over 1.00, indicating that it would sink in water.) With such a wide disparity between specific gravity values, it’s not hard to see how confusing this measurement can become when no qualifying information accompanies the value.

On this website, every effort has been made to use clear and standardised numbers for specific gravity measurements. The first number is the basic specific gravity, based on the botanical standard of oven-dry weight and green volume. The second number is meant for woodworkers, and is simply a snapshot of the wood’s specific gravity at 12% MC, (that is, both 12% MC weight and volume). Water weighs 1,000 kilograms per cubic meter, so taking the wood’s density (in metric units) and dividing by 1,000 yields its specific gravity in woodworking standards. (Reference : Wood Database by Eric Meier)

Spinthout : Sapwood

Sapwood, also called alburnum, outer, living layers of the secondary wood of trees, which engage in transport of water and minerals to the crown of the tree. The cells therefore contain more water and lack the deposits of darkly staining chemical substances commonly found in heartwood. Sapwood is thus paler and softer than heartwood and can usually be distinguished in 

cross sections, as in tree stumps, although the proportions and distinctness of

the two types are variable in different species. Sapwood is sensitive to fungi and is therefore not very usable unless treated chemically. As it has a high water content is is also prone to shrinkage and twisting.

Stamopbouw : Trunk structure.  

Trunk/Stem: The trunk, or stem, of a tree supports the crown and gives the tree its shape and strength. The trunk consists of four layers of tissue. These layers contain a network of tubes that runs between the roots and the leaves and acts as the central plumbing system for the tree. These tubes carry water and minerals up from the roots to the leaves, and they carry sugar down from the leaves to the branches, trunk and roots.

Heartwood: As a tree grows, older xylem cells in the centre of the tree become inactive and die, forming heartwood. Because it is filled with stored sugar, dyes and oils, the heartwood is usually darker than the sapwood. The main function of the heartwood is to support the tree.

Xylem/Sapwood: The xylem, or sapwood, comprises the youngest layers of wood. Its network of thick-walled cells brings water and nutrients up from the roots through tubes inside of the trunk to the leaves and other parts of the tree. As the tree grows, xylem cells in the central portion of the tree become inactive and die. These dead xylem cells form the tree’s heartwood.

Cambium: The cambium is a very thin layer of growing tissue that produces new cells that become either xylem, phloem or more cambium. Every growing season, a tree’s cambium adds a new layer of xylem to its trunk, producing a visible growth ring in most trees. The cambium is what makes the trunk, branches and roots grow larger in diameter.

Phloem/Inner Bark: The phloem or inner bark, which is found between the cambium and the outer bark, acts as a food supply line by carrying sap (sugar and nutrients dissolved in water) from the leaves to the rest of the tree.

Bark: The trunk, branches and twigs of the tree are covered with bark. The outer bark, which originates from phloem cells that have worn out, died and been shed outward, acts as a suit of armour against the world by protecting the tree from insects, disease, storms and extreme temperatures. In certain species, the outer bark also protects the tree from fire.


Sterkte van hout : Wood strength

A collective name for various mechanical characteristics of wood such as toughness, elasticity, bending strength, flexibility under impact, modulus of rupture, strength, compression parallel and perpendicular to the fibre ... etc. We avoid the term ‘strength’ due to it’s inaccuracy.

Modulus of rupture:

(sometimes referred to as bending strength), is a measure of a specimen's strength before rupture. It can be used to determine a wood species' overall strength; unlike the modulus of elasticity, which measures the wood's deflection, but not its ultimate strength.

Stijfheid : Stiffness

Stiffness is the tendency of a material to maintain its original shape and size when external forces are acting upon it, and so to resist deformation.Something that is difficult to deform, is stiff. What changes form easily is flexible. (See also elasticity, and bending strength, in relation to stiffness

Stralen : Rays

Rays are light coloured lines visible at the end surface (end grain). The rays run in a radial direction from the heart of the tree to the cambium. It is radially grown parenchymal tissue.


Taaiheid : Toughness 

Toughness versus brittleness or torsion versus frailty. Tough wood is experienced in practice as wood that is difficult to split. Tough wood is wood that will not break until the wood is completely distorted. Tough wood is that which, even though torn, still hangs together and can be moved back and forth without breaking.Tough wood requires flexibility and has therefore the opposite of fragility.Measurement of the toughness is done by a torsion test, and is expressed in N / mm2.

The timber with tough fibres will twist after substantial and prolonged torsion and bend at right angles to the axis. On the other hand brittle wood will break off suddenly, without warning, during a 

test, after only a light torque.The tear out will be irregular and run obliquely with respect to the axis. 

Tangentiale as : Tangential axis.

One of the three axes in a tree trunk.The tangential axis is perpendicular to the grain, and it affects the growth zones. A cut tangental to the growth rings gives plain wood.

Textuur : Texture.

Texture is the diameter of the wood vessels (xylem) and the height and width of the rays. It is the ratio of the elements of which the timber is constructed, and more specifically the arrangement of the pores. The texture is visible with a x10 magnifying glass. In some books the word ‘grain’ is used but we shall use the word ‘texture’. 

Coarse texture: 

we see large pores; the wood vessels have a sizeable diameter; the rays through the wood are thick. Ex. oak (Quercus pendunculata).

Medium texture: 

Moderately large pores, medium diameter of the xylem vessels and visibility of the rays.

Medium texture: 

Moderately large pores, medium diameter of the xylem vessels and visibility of the rays. Example: Essen (Acer spp).

Trekhout : Tension Wood

Reaction wood; compression wood & tension wood in hardwood.


Vessel : Houtvat

Vezel: Fibre   

(See wood fibre)

Vochtigheidsgraad : Humidity

(Moisture content, green, seasoned, 12%, after measurement)

° Green = wood is recently harvested. The cells are still full of sap. It contains both unbound and bound water. Dry wood which has become completely wet and has soaked up water is in ‘green condition’.

° Doorgewinterd : Seasoned = the wood was harvested earlier and / or cut, and the precise degree of dryness is unknown.

° 28% = The average saturation; water is drained from the cells, but the cell walls are still filled with water. From maximum 28% humidity shrinkage starts to occur and the timber is harder.

° 12% = The wood is air dried to it’s maximum  or dried in a oven to 12% dryness or less.

° Na meting :  After measuring = The wood contains …. % moisture

Volumieke massa : Volumetric mass density;

(see also density expressed in kg/m3, g/cm3 or il./ft.3

Vroeg hout : Early wood or springwood 

(see summer wood)


Warrige draad : Curly grain

The ordering of the cells is very irregular and runs in different directions. Curly gain occurs mostly at branch rings, trunk/root area and large forks in the tree. Birch (Betula pendula) is an example of European species with curly grain in the trunk. Walnut root, has this distinct pattern, and is extracted from the root of the walnut tree (Juglans spp.) Lignum-vitae (Lignum Vitae) is a tropical wood with this grain

Winterhout : Late wood or summer wood.

Winter woods as an  average are denser and darker than summer wood. However, some species exhibit little difference between early and late wood. 

‘Winter’ and ‘summer’ wood are somewhat misleading terms as they say nothing about the season in which the wood is formed.




Zaagrichting :Cutting direction

Wood Cells will appear differently depending on the direction in which the timber was cut. We will consider the primary differences resulting from sawing along three different axis. Sometimes we speak of "the wood is quarter sawn, by which we mean that the growth rings are perpendicular to the the radial plane. However, some flexibility is necessary because the growth rings will always beat a variable angle to the cutting edge. Therefore, we will only speak in terms of the three axes: longitudinal, radial and tangential.

Zachthout : Soft wood (not to be confused with ‘softwood’)

Soft wood is wood with a low density and / or a low specific gravity. 

° Wood with a very low to low density (0-15 to 0-45) will also, almost always, have a low density (kg / m3). Here we find, among others white poplar (Populus alba) 0-40 to 0-46 and European pine (Picea abies 0-34 - 0-41 back, but also white willow (Salix alba) 0-34 to 0-40.

° Wood with a moderate specific gravity is, for example, European cherry (Prunus avium) with 0-48 to 0-60.

° Wood with a high to very high specific gravity, for example, European beech (Fagus sylvatica) 0.53- 0.71. 

European oak (Quercus pedunculata) 0.60-0.80 

or ebony (Diospyros 1:10 to 1:20. 

The latter sinks in water even after it has been dried.

Zomerhout : Early wood or Spring wood

Early wood or spring wood, is the first shaped tissue within a growth zone. If a distinction is visible between summer and winter wood,  then the diameter of the cells in summer wood are bigger than in winter woods and they often have a lighter colour. However, some species show no difference between early and late wood. ‘Winter’ and ‘summer’ wood are somewhat misleading terms as they say nothing about the season in which the wood is formed.

Zwaar hout : Heavy wood

(See specific gravity)