=Packing the Cylinder.=—The cylinders are so constructed that the iron surface does not come in actual contact with the printing paper. In fact, there is a deficiency between the actual and necessary diameter of the cylinder of a few mm., sometimes as much as 7 mm. This is compensated for by the addition to its surface of “packing,” which gives a more elastic pressure than the unyielding surface of iron. This packing is not applied to the entire surface of the cylinder, but is so devised that it exerts pressure upon the surface of the picture only. A sheet of smooth four-ply cardboard is attached to the cylinder by means of thin glue, this first sheet usually exceeding the size of the picture. To this is attached a second piece, cut of the exact size of the image, and attached by means of the glue, forming a raised block in exact register with the position of the picture on the printing plate; this is covered with a thickness or two of fine blotting-paper, and over the whole the sheeting of the cylinder is tightly stretched in the usual well-known manner. It is self-evident that the circumference of the cylinder must traverse at exactly the same speed as the bed of the machine, or there will be a horizontal rubbing or friction between the surface of the printing paper and that of the printing layer, which will result in impressions lacking in sharpness, and ultimate destruction of the plate. =Masking the Prints= for the production of white margins is usually performed by one of two methods, each having advantages and disadvantages which should be carefully considered before adopting either; both are in practical use. In one is used a light rectangular iron framework or “frisket,” conforming to the size of the cylinder, to which it is attached by hinges. This framework is opened and closed automatically, remaining open during the period the cylinder is resting and the inking is taking place. At this point the “layer-on” inserts the paper, it is seized by the grippers, and the masking frame closes down into suitable grooves in the circumference of the cylinder, such grooves being useful to prevent any lateral movement of the frame. To the latter are attached four movable strips of thin zinc, which may be adjusted by means of set screws to form an opening of any desired size. The printing paper being inserted in the grippers, the frame closes, holding the paper upon the cylinder, the strips of zinc at the same time protecting the edges of the paper from immediate contact with the printing layer, the cylinder revolves, and the printing is effected. In large sizes the zinc strips are necessarily of such strength that the edges would cut and damage the printing layer; it is therefore usual to adjust the strips to within about 5 mm. of the edges of the picture, and by attaching strips of varnished tissue paper to the zinc, reducing the aperture to the size of the picture in hand. In large sizes—where