The next few posts are just a basic overview of trying to identify wood, looking at some of the more common characteristics. So if we have an old piece of wood, how do we identify what it is?
The easiest way is to look for distinguishing characteristics, some of which will separate hardwoods from softwoods. These can include rings, pores, grain (long surface), rays, hardness, weight, smell, and colour. First some basics. All wood is designed to carry sap, and it starts life as sapwood. As a tree ages, the inner core of the tree requires more for structural support, and hence the sapwood is modified to become heartwood. An example of a cross-section from an elm tree is shown below. Notice the distinct difference between sapwood and heartwood (this isn’t always the case).
The photograph also shows the grow rings. Both softwood and hardwood have rings, although certain types of trees (e.g. tropical near the equator) lack apparent rings, because the growth cycle is all-year around. In temperate regions, wood is formed only during spring and summer, and the wood formed in the summer differs from that formed in the spring.
Springwood (or earlywood) is usually light in colour, light in weight, and contains numerous tubes to transport sap (i.e pores), and is only moderately strong. When summer takes over from spring, the tree changes the character of the wood it produces. Nutrients can now travel upwards through the springwood, but the tree needs more structural support. Summerwood (or latewood), is usually fibrous, with thick, strong walls, and small cavities – it is often darker in colour. The width of annular growth rings varies depending on water availability, sunshine etc. Fast growing trees may have thick rings, whilst slower growing trees have narrow rings. The other structure most apparent are rays – radial structures which occur perpendicular to the growth rings, used for the radial transport of sap.
The first thing to determine is of course is the wood a hardwood or softwood? A softwood is a coniferous or needle-leaved trees. It is called softwood because it is generally soft and easy to work, and it has a simple structure. A hardwood (deciduous) is a tree that has broad leaves, and is sometimes physically harder than softwoods and also denser. A notable exception is poplar. Here are some basic differences:
- Softwoods have rays that are very narrow, and barely visible.
- Softwoods contain resin (often giving them a characteristic turpentine smell).
- Hardwoods have visible pores.
- Hardwoods often develop large and characteristic rays.