Understanding Wood Grain

Technically, the word grain refers to the orientation of wood-cell fibers. That's quite different from figure, which describes the distinctive pattern that frequently results from various grain orientations. To understand this, it may help to think of the word direction following the word grain. All grain types except straight grain can be a blessing or a curse. Because wood with anything other than straight grain may be sawn to produce sometimes exquisite figure, errant grain becomes a blessing. In structural applications, such as home construction, lumber (mostly softwood) with other than straight grain loses some strength. And hardwood boards without straight grain require extra care in machining to avoid tearout and other reactions.

Grain Means texture, too

Texture means the relative size as well as the amount of variation in size of the wood cells. It's the cells and how they're arranged in bands called rays, and the size and distribution of pores, that make the difference between fine-textured wood and coarse-textured wood. Woodworkers, though, say "fine-grained" and "coarse-grained" rather than use the word texture to describe this characteristic of wood. And you don't have to be a wood technologist to see as well as feel the difference in grain.

To fill or not to fill

When wood finishers refer to a hardwood as open-grained or close-grained, they're talking about the relative size of the pores. This determines whether or not the surface requires application of a filler to get a smoother finish.

It's all in how you view a board

A flatsawn board, that is, one sawn from a log through and through without it being turned, has three surfaces or planes, as shown in the illustration (below). In true quartersawn wood, the log must be sawn lengthwise into quarters. Then, each quarter log has to be sawn perpendicular to the growth rings. Although a quartersawn board has the same planes, its end-, face-, and edge-grain views will look different from a flatsawn board.

A few grainy tailes

Did you know that the cellular structure of red oak is so open that you can blow smoke through it from end-grain to end-grain (flatsawn). Try it.

White oak, on the other hand, has such a tight cell structure that water can't pass. That's why white oak works so well for whiskey barrels and outdoor furniture.

Lignum vitae, a hardwood native to the West Indies, has the finest-grain of any wood known and an ironlike density. A cubic foot of it, air-dried, weighs about 83 pounds-so heavy that it won't float.

Illustrations: Brian Jensen