In the preparation of lumber for use, it is necessary to remove its moisture, after which the wood is seasoned. The planks and boards after sawing are placed in large square piles in the open air, each layer separated by three or four narrow strips or boards laid in the opposite direction. By this means a free circulation of air takes place throughout the pile; the drying is gradual and thorough, if allowed sufficient time. For ordinary carpentry, two years is considered enough, but for joinery at least four years should be allotted to the seasoning. Many processes have been devised to hasten the evaporation - such as kiln-drying, in which the wood is placed in chambers heated by steam, or hot air, or by the employment of vacuum-pumps together with heat. All are inferior, however, to the open-air seasoning, in that they cause a rapid drying of the surface and ends, with a slow or imperfect drying of the interior; thus impairing both the strength and elasticity of the wood.

It is difficult to give rules for testing wood to determine whether "it has been properly seasoned or not. One way is to push a knife-blade into the wood, and note how much it sticks when withdrawn. Another is to cut a shaving from the board, and note its elasticity, brittleness, or strength. Experienced workmen crush shavings in their hands to determine the character of the wood.

As the wood loses its water it shrinks perceptibly, much more in the direction of the annual rings than in the direction of the medullary rays, and very little, if at all, in the direction of the fibers. If we examine the end of a log which has been exposed to the weather, we will find cracks extending from the center toward the circumference, and which penetrate from a few inches to a foot or more into the log (Fig. 14). These cracks, called wind-checks, are seen in planks and boards, and cause the ends to become waste wood. To prevent this rapid drying, the ends of the logs are tarred or painted. If the lumber is piled soon after sawing, these wind-checks are smaller, and the waste portion is consequently less.