PROPERTIES OF WOOD. 



47 



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, bend- 

 ing in the form of a bow, is, 

 so to speak, longitudinal warp- 

 ing. 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. 



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 froro 



Fig-. 41. a, Star Shakes; 6, Heart Shakes; 

 c, Cup Shakes or Ring- Shakes; d, Honey- 

 combing-. 



