Timber characteristics, structure and identification: HSC Industrial Technology Timber Products and Furniture Technologies

What this dot point is asking

In the Timber Products and Furniture Technologies focus area, NESA expects you to understand timber as a material from the inside out. You need to explain how a tree grows, what its internal structure looks like, and how that structure produces the properties you exploit when you design and build. You also need to classify timbers as hardwoods or softwoods and identify the common species used in furniture by their colour, grain, density and working characteristics. This knowledge underpins both the written examination and the material choices you justify in your Major Project folio.

How a tree grows

A tree grows in two directions. It grows taller at the tips and grows thicker through the cambium, a thin layer of living cells just under the bark. Each growing season the cambium lays down a layer of cells: fast, open earlywood in spring and denser latewood later in the season. Together these form the visible annual rings or growth rings you count on a cross section.

Moving inward from the bark you pass through the bark, the cambium, the sapwood and finally the heartwood. Sapwood is the outer living wood that carries sap; it is usually lighter, softer and more prone to decay and insect attack. Heartwood is the inner, older wood whose cells have died and filled with extractives, making it darker, more stable and more durable. For most furniture you want heartwood.

Cellular structure and grain

Wood is made of long cellulose cells bound together by lignin, mostly running up and down the length of the trunk. This directional structure is why timber is far stronger along the grain than across it, and why it splits easily along the grain. Understanding grain direction tells you how to mark out, cut, plane and join timber without tearing or splitting it.

The terms below describe how that structure appears on the surface:

• Grain: the direction and arrangement of the wood cells; it can be straight, interlocked, spiral or wavy.
• Figure: the decorative pattern produced by grain, rings, rays and knots, prized in furniture for its appearance.
• Texture: the relative size of the cells, described as coarse or fine.

Hardwood and softwood classification

Timbers are classified botanically, not by how hard they feel:

• Hardwoods come from broadleaved, mostly deciduous trees such as eucalypt, oak, blackwood and jarrah. They generally have a more complex cell structure and are often, but not always, denser and harder.
• Softwoods come from coniferous, needle-leaved trees such as pine, cedar and hoop pine. They grow faster, are usually lighter and easier to work, and dominate structural and plantation timber.

The classic exception is balsa, a very light timber that is botanically a hardwood. Knowing this distinction matters because the written paper often tests whether you understand that the labels are botanical.

Physical properties that matter for furniture

When you select a species you are really selecting a set of properties:

• Density: heavier timbers are generally stronger and more durable but harder to work.
• Hardness: resistance to denting and wear, important for table tops and floors.
• Stability: how much the timber moves with humidity; some species cup and twist far more than others.
• Durability: natural resistance to decay and insects, which decides whether a timber suits outdoor use.
• Workability: how easily it cuts, planes, glues and finishes.
• Appearance: colour, grain and figure, which drive aesthetic choices.

Identifying common species

Identification combines several clues. You look at colour, examine the grain and figure, judge the weight in your hand, smell freshly cut surfaces and note how the timber works under a tool. Tasmanian oak is pale and straight grained; jarrah is a deep red brown and very hard; blackwood shows rich golden brown figure; radiata pine is pale, light and resinous. Building a mental library of these clues lets you both answer identification questions and choose convincingly for your project.