It may be found sometimes that only some of the sheets are affected. This indicates that, whereas uniform quantities of a solution of sodium sulphite have been served out in all fields, the proportion may have been excessive in the case of fields giving a latex of comparatively low rubber content. What suits the latex from old trees may be excessive probably for the latex of younger trees. This is not an infallible rule, as in the case of older fields in which immature bark is being tapped, it is to be noted that the dry rubber content of latex may be less than that of latex obtained from younger trees.
This type of moist glaze is not easy to remove. Ordinary surface washing had but a temporary effect, and the trouble recurs. The only way of dealing with the difficulty is to soak the sheets for days in running water (or in successive changes of water) and to re-smoke until dry.
(b) The second type of moist glaze is not so difficult to deal with, and may be removed as a rule by washing the sheets when the rubber is otherwise apparently dry.
It appears to be mainly a matter of unsuitable fuel for smoking and of failure to provide adequate ventilation. A large number of estates have been “thinning-out” or are doing so systematically. The logs thus obtained are often used as fuel in the very green stage. The smoke thus generated must be moist, and if the building is entirely closed, this moisture must be deposited eventually upon the rubber and racks. Some estates have surmounted the difficulty by opening up the roof-ridge slightly so as to allow the moisture to escape with some of the smoke; but if the logs from rubber-trees are to be used, they should be stacked in the sun for some time. Even then, preferably, they should not be used alone. A judicious admixture of dead and rotting jungle-timber appears to give very satisfactory results.
Virgin Spots and Patches.—If the description really indicates the defect it simply means that portions of the sheets are not dry. When cut they exhibit the typical whitish, opaque appearance described as “virgin.” It is doubtful whether any rubber put upon the market as No. 1 product nowadays can have this complaint levelled at it. In the extreme case it points to gross negligence on the part of the packer.
Sometimes what are taken to be small spots of “virgin” are really patches of tiny air or gas bubbles. The point can be easily determined by cutting through the patch and examining the cut edges.
Surface Moulds or Mildew.—During the last two years, complaints regarding the incidence of “mouldy rubber” (i.e., relating chiefly to the presence of mildews on the surface) have become increasingly common.
To judge by the comments of producers, who as a rule never again see their rubber after it leaves the estate, one would infer that the defect is imaginary, and that the complaints are made solely with a view to repudiation of contracts or the general cheapening of an article of commerce. They can often point out, with a certain amount of truth, that there has been no change in the methods of preparation or curing, and that previously there were no complaints.
It is forgotten, however, that in former years the smaller output of rubber was taken into consumption more rapidly than of recent years. That is to say, the interval between smoke-curing and the employment of the rubber in the manufacture of goods did not demand such a long period of storage. Hence the effects of smoke-curing are now more likely to vanish.
Going still further back in the history of plantation rubber, we can point to the time when smoked sheets were allowed, or had, to remain in the curing-sheds for very extended periods. Loose specimens of rubber prepared during that decade still exhibit no signs of mildew growth.