This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
These depend greatly upon the treatment of the tree, the time of felling it, and the nature of the soil in which it has grown. Good timber should be from the heart of a sound tree, the sapwood being entirely removed, the wood uniform in substance, straight in fibre, free from large or dead knots, flaws, shakes, or blemishes of any kind. If freshly cut, it should smell sweet; the surface should not be woolly, nor clog the teeth of the saw, but firm and bright, with a silky lustre when planed; a disagreeable smell betokens decay, and a dull chalky appearance is a sign of bad timber. The annual rings should be regular in form; sudden swells are caused by rind-galls; closeness and narrowness of the rings indicate slowness of growth, and are generally signs of strength. When the rings are porous and open, the wood is weak, and often decayed. The colour should be uniform throughout; when blotchy, or varying much from the heart outwards, or becoming pale suddenly towards the limit of the sapwood, the wood is probably diseased. Among coloured timbers, darkness of colour is in general a sign of strength and durability. Good timber is sonorous when struck; a dull, heavy sound betokens decay within. Among specimens of the same timber, the heavier are generally the stronger.
Timber for important work should be free from defects. The knots should not be large or numerous, and on no account loose. The worst position for large knots is near the centre of the balk required, more especially if forming a ring round the balk at one or more points. Though the sapwood should be entirely removed, the heart of trees having most sapwood is generally strongest and best. The strongest part of the tree is usually that containing the last-formed rings of heartwood, so that the strongest scantlings are got by removing no more rings than those including the sapwood. Timber that is thoroughly dry weighs less than green; it is also harder and more difficult to work.