The forming or laying the grained surface, technically called _ground_, is necessarily of the utmost importance, and is effected by a tool known amongst practical workers as "the rocker," called also "cradle," or "berceau"--the French equivalent--from the peculiar rocking motion given to it by the operator. The rocker is made of moderately thin and carefully tempered steel about two inches broad, and might be termed a stumpy, wide chisel were it not that it is curved (like a cheese-cutter) and notched or serrated at the cutting edge, which serration is caused by one side of the steel being indented into small fluted ridges running parallel upwards to the handle by which the tool is held, and somewhat presenting the appearance of a small-tooth-comb. On the plain smooth side the rocker is ground level to the edge, like other cutting tools, and sharpened on a stone or hone of suitable quality. In laying the ground this instrument is held firmly in the hand, the elbow resting on a convenient cushion, the serrated cutting edge placed on the plate with a slight inclination, and a steady rocking motion given to the tool, which slowly advances over the surface of the copper or steel, forming on its way a narrow indented path. Side by side with this path another is made until the whole surface of the plate has been covered. The series of parallel paths is then repeated at a certain angle over the previous ones, and so on in regular progressive angular order until the required closeness of texture has been produced; to do this it is necessary that the series of parallel paths--technically called a _way_--should be repeated in proper angular progression from sixty to a hundred times. As the continual friction of the elbow against the cushion caused the laying of a ground to become a severe and painful operation, particularly when the use of steel instead of copper plates came into practice early in the present century, a modification of this plan was introduced whereby the tool was fixed at the fitting angle into one end of a long pole, the other end being inserted loosely in a ring fixed on the board upon which the plate was placed; the requisite rocking motion could then be easily given by the hand, and much painful labour avoided. The necessity for a good ground being so great, as the process became more and more general in England, a race of professional ground-layers grew up, who were paid at a certain rate per square inch for the surface thus covered. Much controversy has taken place as to the means by which Siegen, Prince Rupert, and the earlier mezzotinters produced their grounds, but there is little doubt that it must have been accomplished by some rude form of the present tool, and the curious appearance of the grain--as seen in very early mezzotints--must have been caused by the irregular crossings of the impressed layers, the necessity of regular angular procedure throughout the plate, in order to obtain an