Woods we see in everyday American life—pine, oak, and maple—make up a small and comparatively uninteresting group of species. Around the globe, however, woods vary widely in appearance and physical properties. Colors can range from pale yellows and grays to vibrant hues of purple, red, and green, and from rich browns to pure, solid black.
Some species, like certain pines, are so abundant that they are used as disposable packaging material, while others, such as African Blackwood, are so rare that they can cost over $600.00 per cubic foot!
Density can vary from unbelievably light—balsa is less than 1/6th the density of water—to heavier than concrete. For example, the South American species Lignum Vitae is so water-resistant and dense that it is commonly used in bearings for large naval craft and hydroelectric dams.
In order to fully understand these differences, and how they can affect your projects, I will cover some of the basic differentiating properties of wood and the terminology used to describe them.
Grain type is another important factor to consider. Straight grained wood is predictable and easy to cut and sand, whereas interlocked grain (wood that regularly changes its growth direction slightly, causing the layers of growth to interlock and overlap) can cause unwanted 'tearout' during cutting, planing, and/or sanding, as seen on the maple board on the far left below. This tearout occurred when I was trying to plane down the edge of the board—the blade caught a section of grain that was interlocked with the surrounding wood, tearing out the entire area instead of cutting straight across as I had intended.
Porosity affects both the appearance and working properties of the wood. Ring-porous woods have larger pores at the edge of their growth rings, while diffuse-porous woods have the same size of pores throughout. This can affect the appearance of the wood, especially in pieces that are flatsawn, as shown below. Additionally, woods that are highly porous are harder to sand to a smooth finish, and tend to absorb more glue and finish than less porous woods.