These indiarubber rollers are not suited for the first inking of the plate, but are invaluable for rolling up the half-tints of the collotype plate. As they somewhat readily take colour off the plate they must be first rolled up in a thinner ink and a separate slab. According to “Lithographia” these indiarubber rollers may be cleaned with lye, or strong alcoholic spirit. If cleaned with turpentine it may be advantageously followed by rinsing with soap and water; by so doing the application of French chalk is unnecessary. These rollers are, by comparison with others, nearly indestructible, and therefore cheap, notwithstanding their high first cost. [Illustration: _Fig. 5._] =Velvet Rollers= have latterly come much into use, and are very successfully used for inking-up the transfers in photo-lithography. They may be also used in photo-xylography and photo-ceramic processes, and also for certain purposes in collotype. A necessary precaution is that the seam of the velvet should always be kept off the surface subjected to the rolling, and this may be carried out if the roller is, say, 10-1/2 centimetres in diameter, a length of 31·2 centimetres may then be rolled without using the seam. The sketch will explain the construction. The cylinder or stock is of pear-wood, and the handles of box; first covering serge, which before sewing on should be well shrunk in hot water; over this comes the velvet, the edges of which must not overlap, but must be drawn together as close as possible by means of thread. One advantage of this roller is that it is ready for immediate use; it must, after use, be carefully cleaned before being placed aside; this is best done by repeated rollings on a clean slab, and the judicious application of a little turpentine. Turpentine only may be used to thin ink for use with this roller. =Drying Rollers.=—In addition to those already enumerated, all of which are intended for the application of the ink to the plate, other rollers are required, similar in construction, but covered with wash-leather or cloth, and used for the purpose of absorbing superfluous moisture. For these it is necessary, or at least advisable, that the frames be so constructed that the rollers may be readily removed when by continued use they have become too damp. This method of drying the plates is far preferable to the customary one of wiping with a cloth, for even with the greatest care, if the printing should extend over hundreds of copies, the layer upon the plate will inevitably get scratched when wiping or rubbing is resorted to, especially if isinglass—which tends to soften the film—be present. =Palette Knife or Spatula.=—It is unnecessary to describe; they are used for mixing the ink and applying it to the slab and rollers, and for cleaning the latter. They may be either of hard wood or metal. =The Ink Slab= may be either of slate, a lithographic stone, or a sheet of strong zinc securely attached to a block of wood truly planed.