After pressing, the next step is to sew the sheets on to cords or twine, set vertically at proper distances in a frame, called a "sewing bench," for this purpose. No book can be thoroughly well bound if the sewing is slighted in any degree. Insist upon strong, honest linen thread--if it breaks with a slight pull it is not fit to be used in a book. The book is prepared for the sewer by sawing several grooves across the back with a common saw. The two end grooves are light and narrow, the central ones wider and deeper. Into these inner grooves, the cords fit easily, and the book being taken, sheet by sheet, is firmly sewed around the cords, by alternate movements of the needle and thread, always along the middle of the sheet, the thread making a firm knot at each end (called the "kettle-stitch") as it is returned for sewing on the next sheet. Sometimes the backs are not sawed at all, but the sheets of the book are sewed around the cords, which thus project a little from the back, and form the "bands," seen in raised form on the backs of some books. Books should be sewed on three to six cords, according to their size. This raised-band sewing is reckoned by some a feature of excellent binding. The sunken-band style is apt to give a stiff back, while the raised bands are usually treated with a flexible back. When sewed, the book is detached from its fellows, which may have been sewed on the same bench, by slipping it along the cords, then cutting them apart, so as to leave some two inches of each cord projecting, as ends to be fastened later to the board. In careful binding, the thread is sewed "all along," _i. e._: each sheet by itself, instead of "two on," as it is called. The next process is termed "lining up," and consists of putting on the proper fly-leaves or end-leaves, at the beginning and end of the volume. These usually consist of four leaves of ordinary white printing paper at each end, sometimes finished out with two leaves of colored or marbled paper, to add a touch of beauty to the book when opened. Marbled paper is more durable in color than the tinted, and does not stain so easily. One of these end-leaves is pasted down to the inside cover, while the other is left flying--whence "fly-leaf."