Common Wood Defects
Bow: A curve along the face of a board that usually runs from end to end.
Cup: Warping along the face of a board from edge to edge.
Twist: Warping in lumber where the ends twist in opposite directions.
Split/Check: Breaks at the end of a board that run along the grain. Checks and splits are usually restricted to the end of a board.
Tight knot: A knot fixed by growth or position in the wood structure so that it firmly retains its place in the surrounding wood.
Loose Knot: A knot that cannot be relied upon to remain in place in the piece. Caused by a dead branch that was not fully integrated into the tree before it was cut down.
Wane: The presence of bark or absence of wood on corners of a piece of lumber.
Crook: Warping along the edge from one end to the other. This is most common in wood that was cut from the center of the tree near the pith.