Formerly the diamonds were picked out from the concentrates by means of the keen eyes of skilled natives; but the process has been vastly simplified and the risk of theft entirely eliminated by the remarkable discovery made in 1897 by F. Kirsten, of the De Beers Company, that of all the heavy constituents of the blue ground diamond alone, with the exception of an occasional corundum and zircon, which are easily sorted out afterwards, adheres to grease more readily than to water. In this ingenious machine, the ‘jigger’ or ‘greaser’ (Plate XXIII) as it is commonly termed, the concentrates are washed over a series of galvanized-iron trays, which are covered with a thick coat of grease. The trays are slightly inclined downwards, and are kept by machinery in constant sideways motion backwards and forwards. So accurate is the working of this device that few diamonds succeed in getting beyond the first tray, and none progress as far as the third, which is added as an additional precaution. The whole apparatus is securely covered in so that there is no risk of theft during the operation. The trays are periodically removed, and the grease is scraped off and boiled to release the diamonds, the grease itself being used over again on the trays. This is the first time in the whole course of extraction from the mines that the diamonds are actually handled. The stones are now passed on to the sorters, who separate them into parcels according to their size, shape, and quality. [Illustration: _PLATE XXIII_ DIAMOND-SORTING MACHINES] [Illustration: _PLATE XXIV_ KAFIRS PICKING OUT DIAMONDS]