DEFINITION OF HEARTWOOD: The older harder nonliving central wood of trees that is usually darker, denser, less permeable, and more durable than the surrounding sapwood. It is the dead, central wood of trees. Its cells usually contain tannins or other substances that make it dark and sometimes fragrant. Heartwood is mechanically strong, resistant to decay, and less easily, or not at all, penetrated by wood-preservative chemicals than other types of wood. One or more layers of living and functional sapwood cells are periodically converted to heartwood.
|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 color.
However, color in wood can be very misleading; not all heartwood is dark and not all dark-colored 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, a more complete understanding is needed of what wood is and how both sapwood and heartwood form.
The outer, lighter colored wood is the sapwood. This is the "working" part of the tree, as water and sap will flow through the sapwood much like blood through your arteries, veins and capillaries. While this part of the trunk is vital to the tree when it is living, it doesn't make for very good stock for woodworking. Sapwood contains a lot of moisture, will shrink considerably when dried, and is much more susceptible to termites, bugs and fungus.
The inner, darker section of the trunk is the heartwood. Heartwood is formed from old, "retired" sapwood, and becomes the strong spine of the tree. Heartwood is preferred by woodworking companies, as it is far less susceptible to decay and fungus and doesn't contain nearly as much moisture as sapwood, which means it will shrink less when dried. In addition the heartwood of many wood species is termite resistant such as Bangkirai which we use for our elements which could be attacked by termites.
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. In general, more vigorously growing trees tend to have wider bands of sapwood.
The sapwood-heartwood distinction has important implications for woodworking companies beyond the obvious implications of color. In general only an expert can properly indicate the difference between sapwood and heartwood. The non-expert may apply some simple rules: Heartwood in genera lhas a darker color, the growth rings are closer together and the radii of these rings are smaller.
Beam made from sapwood taken from a log with distinctive difference in color between sapwood and heartwood
Beam made from heartwood taken from a log with distinctive difference in color between sapwood and heartwood
Heartwood wood has darker color and smaller radii
Beam made from sapwood taken from a log without distinctive difference in color between sapwood and heartwood
Beam made from heartwood taken from a log without distinctive difference in color between sapwood and heartwood
Heartwood wood has light color but smaller radii
More information here: <termites and heartwood>