INTRODUCTION. 



confused with the above. " Silver-grain " refers to the 

 distinct patches of medullary rays often seen on those 

 surfaces which coincide more or less with the radial 

 plane. 



Since the workman has to think of his tools, and 

 their edges, teeth, etc., as well as of the wood he uses, 

 he comes to look critically at the relative hardness or 

 otherwise of the latter ; and the kind of surface — smooth, 

 lustrous, silky, clean, mottled, etc. — he can bring out 

 with such instruments as the chisel and plane, also in- 

 fluences his verdict as to the quality of the timber. Some 

 varieties of the Scotch Pine, for instance, are so resinous 

 that the tools clog and refuse to work up a fine surface, 

 whereas the beautiful silky lustrous surface of properly 

 planed White Deal (Spruce) is well known to every 

 joiner as easy " to work." 



Similar considerations affect the cabinet-maker, etc., 

 who wants a good polishing surface ; and he knows that 

 not every smooth wood-surface will take stains or polish 

 — and the remark applies to painting. The turner and 

 the carver are also critical as to the hardness, smooth- 

 ness, ease of working, etc., of the woods they use. It 

 is also important to these, and others who use wood, 

 whether the timber consists chiefly of heart-wood or 

 of sap-wood : the latter is usually darker, harder, and 

 heavier, but more durable and closer in texture. Con- 

 siderations of colour also affect the question, and so do 

 those of the power to hold nails. 



Some woods contain so much tannic and other acids 

 that the iron of the nails becomes corroded — by chemical 

 action between the metal and the acids — and the nails 

 soon drop out ; other woods are difficult to nail, because 

 they split so readily as the point is hammered in ; 

 others, again, are apt to warp and twist, and so prize 



