When purchasing rough lumber, you may see the wood listed as Plain sawn, quarter sawn or rift sawn. Theses are simply different methods for extracting boards from a log.
The most simple method for milling a log into planks, plain sawing, involves making a series of parallel cuts through the log. This method is quick and leaves the least amount of waste. Because of the directional tension across the grain as the wood dries, ages and wears, flat sawn boards can be subject to cupping, twisting and bowing. Often, dry boards will absorb moisture from the atmosphere and will become distorted. Plain sawn lumber has a large variety of appearances based on the angle of the growth rings relative to the surface of the board. Often, these rings can be nearly parallel to the board, creating large, open patterns. When the angle of the growth rings nears perpendicular to the surface of the board, there are tighter stripes across the face of the plank.
To create quarter sawn lumber, the log is first cut radially into four quarters. Once quartered, there are two different ways in which boards are extracted from the log as shown in the photo below. The upper method is more complex and labor intensive, but leaves far less waste from the log. The method on the right hand side can be executed quickly, simply plain sawing the quartered log. However, this technique leaves large amounts of waste wood. In a quarter sawn board, the growth rings of the tree are closer to perpendicular to the surface of the board than in most plain sawn boards. In certain species of wood, most notably Oak, this creates a beautiful visual effect. We stumbled upon this great blog post on quarter sawn oak. These boards are more stable than plain sawn, being less susceptible to distortion that comes with expansion and contraction from absorbing and releasing atmostpheric moisture. Stable quarter sawn lumber is often recommended for flooring in high moisture, high traffic areas like restaurants, bars and home kitchens.
The most stable boards, and also the most wasteful to produce, are rift sawn planks. Each of these boards is cut radially perpendicular to the growth rings of the tree. There are large triangles of waste left from between each board. As a result, rift sawn lumber is costly to produce and therefore, the most expensive type of planks available from a log.