Grain is the alternating regions of relatively darker and lighter wood resulting from the differing growth parameters occurring in different seasons (i.e., growth rings). The term is used in several ways. Perhaps most important is that in woodworking techniques (e.g. against the grain). In describing the application of a woodworking technique to a given piece of wood, the direction of the technique may be:
- with the grain (easy; giving a clean result)
- against the grain (heavy going; giving a poor result such as chipping or tear-out)
- across the grain (direction of cut is across the grain lines, but the plane of the cut is still aligned with them)
- end grain (at right angles to the grain, for example trimming the end of a plank)
Grain alignment must be considered when joining pieces of wood, or designing wooden structures. For example, a stressed span is less likely to fail if tension is applied along the grain, rather than across the grain. Grain direction will also affect the type of warping seen in the finished item.
In describing the alignment of the wood in the tree a distinction may be made. Basic grain descriptions and types include:
- straight - grain which runs in a single direction, parallel to the axis of the tree
- spiral - grain which spirals around the axis of the tree
- interlocked - grain which spirals around the axis of the tree, but reverses its direction regularly,[clarification needed] alternating, interlocking
In addition, there are a few special grain alignments. Their rarity often promotes the value of both the raw material, and the finished work it becomes a part of. These include:
- bird's eye
In a wider sense, the term grain may also be applied to the orientation of the cut, the way a given piece of wood has been sawn:
- flat-grain: flat-sawn, slab-sawn, or plain sawn,
- edge grain: quarter-sawn or rift-sawn or straight-grained, and
- end grain: the grain of wood seen when it is cut across the growth rings.
Strictly speaking, grain is not the same as the "figure" of wood.
There is irregular grain in burr wood or burl wood, but this is result of very many knots.
- Wood Movement, WoodworkDetails.com
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