We all know to avoid lumber with large, loose knots, and twisted, warped, split, cupped or checked lumber... but how do you tell which boards will most likely do those bad things AFTER you buy them and use them? Here are some photos to show you what to look for and what to avoid. The pieces on the left are desirable and those on the right side of the photos are to be avoided. This is based on how wood behaves depending on ring shape, density and orientation. The last photo shows you what the pith looks like on the face rather than end of the board.