In consequence of the great number of marks used in the timber trade, the difficulty of ascertaining what they mean, and the frequent changes that take place in them, the practical engineer or builder, as a rule, judges of the quality of the timber more by its appearance than by the way in which it is marked.

The characteristics of good timber and the defects to be avoided are given in general terms at p. 360, but a few remarks on selecting balks and deals may be useful. 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.

In the best American yellow pine and crown timber from the Baltic there should be no visible imperfections of any kind.

In the lower qualities there 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. If on the same side of a balk sap is visible at one end and heart at the other, it shows that the heart is wandering; in good timber the "spine" or heartwood should be visible on all four sides. Again, the heart may be twisted throughout the length of the tree. In this case the annual rings which run parallel to two 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 of these 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 the 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 (see p. 400).