Warping is uneven shrinkage, one side of the board contracting more than the other. Whenever a slash board warps under ordinary conditions, the convex side is the one which was toward the center of the tree. However, a board may be made to warp artificially the other way by applying heat to the side of the board toward the center of the tree, and by keeping the other side moist. The board will warp only sidewise; lengthwise it remains straight unless the treatment is very severe. This shows again that water distends the cells laterally but not longitudinally. The thinning of the cell walls due to evaporation, is thus seen to have three results, all included in the term "working," viz.: _shrinkage_, a diminution in size, _splitting_, due to the inability of parts to cohere under the strains to which they are subjected, and _warping_, or uneven shrinkage. In order to neutralize warping as much as possible in broad board structures, it is common to joint the board with the annual rings of each alternate board curving in opposite directions, as shown in _Handwork in Wood_, Fig. 280, _a_, p. 188. Under warping is included bowing. Bowing, that is, bending in the form of a bow, is, so to speak, longitudinal warping. It is largely due to crookedness or irregularity of grain, and is likely to occur in boards with large pith rays, as oak and sycamore. But even a straight-grained piece of wood, left standing on end or subjected to heat on one side and dampness on the other, will bow, as, for instance a board lying on the damp ground and in the sun. [Illustration: Fig. 41. _a_, Star Shakes; _b_, Heart Shakes; _c_, Cup Shakes or Ring Shakes; _d_, Honeycombing.] Splitting takes various names, according to its form in the tree. "Check" is a term used for all sorts of cracks, and more particularly for a longitudinal crack in timber. "Shakes" are splits of various forms as: _star shakes_, Fig. 41, _a_, splits which radiate from the pith along the pith rays and widen outward; _heart shakes_, Fig. 41, _b_, splits crossing the central rings and widening toward the center; and _cup_ or _ring shakes_, Fig. 41, _c_, splits between the annual rings. _Honeycombing_, Fig. 41, _d_, is splitting along the pith rays and is due largely to case hardening. These are not all due to shrinkage in drying, but may occur in the growing tree from various harmful causes. See p. 232. Wood that has once been dried may again be swelled to nearly if not fully its original size, by being soaked in water or subjected to wet steam. This fact is taken advantage of in wetting wooden wedges to split some kinds of soft stone. The processes of shrinking and swelling can be repeated indefinitely, and no temperature short of burning, completely prevents wood from shrinking and swelling.