TIMBER 



115 



comply with this condition, and in most cases it can only be approxi- 

 mated to. 



Characteristics of Good Timber. — Good timber should be uniform 

 in colour and substance ; straight grained ; free from large and dead 

 (or loose) knots, shakes (or cracks), and blemishes of any kind. It 

 should be well seasoned, i.e. the sap should be entirely absent, and 

 when cut with a saw the saw should not clog and the cut surfaces 

 should not appear woolly or dull ; on the contrary they should possess 

 a shiny and firm appearance. Freshly cut surfaces should emit 

 the characteristic odour of the timber in question. The annual rings 

 should be of regular form; narrow rings indicate strength. Timber, 

 when struck, should give forth a clear ringing sound; a heavy, dull 

 sound indicates decay. 



Types of Shakes.— Different types of shakes are illustrated by Figs. 

 114, 115, and 116. 



Fig. 114. 



Fig. 115. 



Fig. 116. 



Fig. 114 shows star shakes, caused by the shrinkage of the wood 

 in a direction parallel to the annual rings. 



Fig. 115 illustrates a common type of shake known as a heart 

 shake. 



Fig. 116 shows cup shakes which are caused by separation of the 

 wood-layers at the junction of two annual rings. 



The last-mentioned type of shake is much more serious than 

 the others, which are usually confined to short lengths at the ends 

 of a log, whereas cup shakes may extend for long distances into 

 the log. 



Seasoning. — After the tree is felled, some process must be followed 

 in order to get rid of the sap. This is known as seasoning. For the 

 purposes of this book only two methods of seasoning need be mentioned 

 viz. : — air seasoning, and water seasoning. 



Trees, which are destined to provide timber for building or other 

 farm purposes, should be felled in late autumn or winter, when the 



