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.
The principal natural defects in timber, caused by vicissitudes of climate, soil, etc, are: - "Heartshakes": splits or clefts in the centre of the tree; common in nearly every kind of timber; in some cases hardly visible, in others extending almost across the tree, dividing it into segments; one cleft right across the tree does not occasion much waste, as it divides the squared trunk into 2 substantial balks; 2 clefts crossing one another at right angles, as in Fig. 217, make it impossible to obtain scantlings larger than 1/4 the area of the tree; the worst form of heartshake is when the splits twist in the length of the tree, thu3 preventing its conversion into small scantlings or planks. "Starshakes": in which several splits radiate from the centre of the timber, as in Fig. 218. "Cupshakes" : curved splits separating the whole or part of one annual ring from another (Fig. 219); when they occupy only a small portion of a ring they do no great harm. "Rind-galls": peculiar curved swellings, caused generally by the growth of layers over the wound remaining after a branch has been imperfectly lopped off. "Upsets": portions of the timber in which the fibres have been injured by crushing. "Foxiness": a yellow or red tinge caused by incipient decay. "Doatiness": a speckled stain found in beech, American oak, and others.
The large trees of New South Wales, when at full maturity, are rarely sound at heart, and even when they are so, the immediate heartwood is of no value, on account of its extreme brittleness. In sawing up logs into scantlings or boards, the heart is always rejected. The direction in which the larger species split most freely is never from the bark to the heart (technically speaking, the "bursting way"), but in concentrie circles round the latter. Some few of the smaller species of forest trees are exceptions to this rule; such as the different species of Casuarina, Banksia, and others belonging to the natural order Proteaceae. They split most freely the "bursting way," as do the oaks, etc, of Europe and America. A very serious defect prevails amongst a portion of the trees of this class, to such an extent as to demand especial notice here. It is termed "gum-vein," and consists simply in the extravasation, in greater or less quantity, of the gum-resin of the tree, in particular spots, amongst the fibres of woody tissue, and probably where some injury has been sustained; or, which is a much greater evil, in concentric circles between successive layers of the wood.
The former is often merely a blemish, affecting the appearance rather than the utility of the timber; but the latter, when occurring frequently in the same section of the trunk, renders it comparatively worthless, excepting for fuel. In the latter case, as the wood dries, the layers with gum veins interposing separate from each other; and it is consequently impracticable to take from trees so affected a sound piece of timber, excepting of very small dimensions. The whole of the species of Angophora, or apple-tree, and many of the Eucalypti, or gums, are subject to be thus affected; and it is the more to be regretted, because it appears to be the only reason why many of the trees so blemished should not be classed amongst the most useful of the hard woods of the colony.
In selecting balks and deals, it should be remembered that most defects show better when the timber is wet. Balk timber is generally specified to be free from sap, shakes, large or dead knots and other defects, and to be die-square. The best American yellow pine and crown timber from the Baltic have no visible imperfections of any kind. In the lower qualities is either a considerable amount of sap, or the knots are numerous, sometimes very large, or dead. The timber may also be shaken at heart or upon the surface. The wood may be waterlogged, softened, or discoloured by being floated. Wanes also are likely to be found, which spoil the sharp angles of the timber, and reduce its value for many purposes. The interior of the timber may be soft, spongy, or decayed, the surface destroyed by worm holes, or bruised. The heart may be "wandering" - that is, at one part on one side of the balk, at another part on the other side. This interrupts the continuity of the fibre, and detracts from the strength of the balk. Again, the heart may be twisted throughout the length of the tree. In this case, the annual rings which run parallel to 2 sides of the balk at one end run diagonally across the section at the other end. This is a great defect, as the wood is nearly sure to twist in seasoning.
Some defects appear to a certain degree in all except the very best quality of timber. The more numerous or aggravated they are, the lower is the quality of the timber. Deals, planks, and battens should be carefully examined for freedom (more or less according to their quality) from sap, large or dead knots, and other defects, also to see that they have been carefully converted, of proper and even thickness, square at the angles, etc. As a rule, well-converted deals are from good timber, for it does not pay to put much labour upon inferior material. The method in which deals have been cut should be noticed, those from the centre of a log, containing the pith, should be avoided, as they are likely to decay.