When they are stacked upright the planks are inclined alternately on opposite sides of a timber rack. The thickness of the timber in this case will separate the planks throughout their whole length, except where they cross. This mode of stacking, though taking more space, is handier, for the timber has to be frequently turned, and is more accessible in the timber rack than when stacked horizontally.

If timber is dried too rapidly it becomes dry outside while it is still very wet inside, and consequently splitting in contraction from the outsides in the direction of the medullary ray ensues, and, if in excess, spoils the whole piece of wood.

The length of time for due seasoning cannot well be exceeded, as it must be remembered that perfect drying is impossible, and the longer timber is exposed to a free drying air the better it becomes.

As a general rule oak in logs 24 ins. square and upwards should be seasoned for two or three years, and the northern pine, to take a more readily seasoned timber, requires for a similar size about half this time. Smaller sizes, of course, will take proportionately shorter times.

Loss of weight is the chief means of measuring the success of the seasoning. Timber is usually seasoned when it has lost from one-fifth to one-third of its weight, but much depends upon the purpose for which it is required.

Water Seasoning

In order to season timber more rapidly than by the natural process, and yet cheaply, timber is frequently submerged in running water, with its fibres in the direction of the stream. The action of the water is to wash out the active portion of the sap, leaving the log merely saturated with water. This takes usually about a fortnight, and afterwards the log has only to be dried in the same manner as in natural seasoning. Partial submersion causes irregular and partial seasoning, and is very harmful. The drying after water seasoning is comparatively rapid, and consequently the timber must be turned daily, to prevent warping and twisting.

Timber which has been water seasoned is less liable to warp or twist than wood naturally seasoned, but is not so durable or elastic. If immersed in salt water the timber is better than from fresh or brackish water, but there is danger from the attack of sea parasites.

Hot Air Seasoning

This is another common process.

The timber is placed in an oven, or hot current of air.

The tendency to cause splitting by contraction in the fast-drying outer rings, while the inner portion of the heart-wood is still 'green,' is very great, and for this reason the timber is usually cut up into planks or other marketable forms before seasoning.

The planks offer a much larger surface area compared with their cubic measurement than logs, and the contrast in the conditions of the outer and inner portions is, therefore, not so marked.

The tendency to splitting is, however, always great, and for this reason the ends of the pieces of timber are usually clamped. The hot air process, as might be imagined, is rapid in its action. It usually takes about a fortnight, but it is expensive.

Wood which has been hot air seasoned loses more of its elasticity and durability than if 'naturally' seasoned, but is not, perhaps, so liable to further shrinkage after being wrought.

To obtain small pieces of timber as nearly perfect as possible, the pieces are entirely desiccated by hot air.

Gunstocks are treated in this way, as the slightest subsequent swelling or shrinkage under the varied temperatures to which rifles are exposed would possibly have a serious effect on the delicate adjustments of the mechanism.

Timbers are usually somewhat bleached by the process of hot air seasoning.

Hot Water Seasoning And Steaming

These are rapid but expensive methods which are somewhat undesirable, as decreasing the durability and elasticity of timber. The liability to dry rot is, however, not so great when wood has been seasoned in this way.

Smoke drying, in a moist warm atmosphere, is an excellent but costly form of seasoning. It is not adopted to any considerable extent.

Of the various methods described the 'natural' is undoubtedly the best. All the other forms of seasoning, in a greater or less degree, destroy the natural properties of good timber, and are chiefly used on account of their speed.

Even when well seasoned, it must not be understood that, for every purpose, the wood is perfectly ready for use. Another final second seasoning is necessary if the wood is wanted for use in fine work, where shrinkage would cause unsightly opening of joints and splitting, when held forcibly in position, like the panel of a door.

The first seasoning would be amply sufficient for the heavier parts of carpenter's work or for out-of-door exposure.

Second Seasoning

In some woods, when a very small amount of the surface timber is removed, warping and twisting will set in almost as if the wood had not been seasoned at all; to prevent this a final second seasoning is resorted to. Timber wanted for good work is then wrought to its general shape and kept if in one piece, or put together temporarily if in several jointed pieces. This roughly made work is then put by in a room at a temperature of about 90°, and kept for periods varying from a fortnight to three months, according to the particular kind of wood and the purpose for which it is required.