Preparations for tapping the trees are generally begun when the plantation has reached an age of four or five years from planting. In each field over a certain age usually not less than four and a half years the trees are measured and numbered. All trees over a certain girth usually not less than 18 inches at three feet from the ground are then marked out for tapping on one or other of the systems presently to be described. The age at which the trees can first be tapped is largely determined by the thickness of the available bark. Experience has shown that trees of 18 inches girth and upwards can generally be lightly tapped without injury. This size, as we have seen, corresponds to an age of from four to six years. At this age the bark has reached a thickness which is capable of sustaining the effects of careful tapping and of making a satisfactory-renewal, whilst yielding a certain amount of latex. From trees of a smaller size than this the yield hardly repays the cost of tapping, and the risk of serious injury is great owing to the thinness of the bark. If the planter can afford to wait until the trees have reached a somewhat larger girth so much the better.
Before describing methods of tapping in detail, we may give a general account of the ordinary routine of an estate on which the harvesting of the rubber is in progress. A start is made in the very early morning, since the earlier the trees are tapped the more freely does the latex flow. Each tapper has a certain number of trees assigned to him or her. In some cases each worker is allotted the task of tapping a certain number of trees and is paid by the day. On other estates payment is made according to the quantity of rubber obtained. In such cases each tapper has the run of a somewhat larger area. In either case the quality of the work performed requires thorough supervision, since the least carelessness in tapping may lead to serious injury of the bark. At the first round the trees are tapped and collecting cups of tin, glass or coconut-shell are placed in position to receive the latex. When the tapping round is completed, the coolie makes a second round provided with a pail of enamelled iron, into which the contents of the several cups are poured. The latex is carried to the factory, where the quantity obtained by each tapper or group of tappers may be separately coagulated, and the wet rubber weighed, before it passes on into the general stock. A third round may then be made in order to scour the cups and to collect the scrap rubber which has congealed in the cups or upon the bark of the tree. More often this work is relegated to a less experienced hand. Periodically also the shavings of bark which have fallen upon the ground are collected, and even the earth upon which latex may have trickled is not wasted; from both these sources low grades of rubber are extracted in the factory.
Tapping processes may be divided into methods of incision and methods of excision. In the excision or paring methods, which are almost universally employed in practice on estates, a thin shaving of bark is removed from the tree at each tapping. Incision methods are designed to extract the latex by pricking or gashing without removal of bark.
Methods of incision or pricking have many points to recommend them, at least in theory. If we are to credit the dictum of Mr Herbert Wright, that the best method of tapping is the one which leads to the greatest flow of latex with the least possible removal of bark, a pricking system in which no bark is removed should be superior to any method of paring. There are however many other points to be taken into consideration besides the flow of latex and the removal of the bark. It may therefore prove instructive to discuss the disadvantages under which some systems of pricking labour as compared with good paring. From such a discussion we may hope to arrive at an understanding of the features which should characterise an ideal system of pricking.
The method of incision was employed by Trimen in Ceylon prior to 1888, but the precise method adopted was not exactly specified. Among the earliest methods of incision practised upon planted trees, of which we have a satisfactory record, was the one employed by Parkin in experiments at Henaratgoda. Parkin's method, which was based on those used in the collection of wild rubber in Brazil, was to make V-shaped cuts in the bark by the aid of a hammer and chisel. With this method two definite defects are associated in practice. A separate collecting cup is required for each V, whilst the surface of the tree becomes rough and lumpy owing to the irregular renewal thus induced, until further tapping becomes a difficult matter. Moreover, except in the case of old trees with very thick bark, it is impossible to avoid more or less extensive injury to the cambium. The method is quite unsuitable for young trees.