After this comes the cutting of the book at the edges. This is done by screwing it firmly in a cutting-machine, which works a sharp knife rapidly, shaving off the edges successively of the head, front and end, or "tail" as it is called in book-binding parlance. This trimming used to be done by hand, with a sharp cutting knife called by binders a "plough." Now, there are many forms of cutting machines, some of which are called "guillotines" for an obvious reason. In binding some books, which it is desired to preserve with wide margins, only a mere shaving is taken off the head, so as to leave it smooth at the top, letting the front and tail leaves remain uncut. But in case of re-binding much-used books, the edges are commonly so much soiled that trimming all around may be required, in order that they may present a decent appearance. Yet in no case should the binder be allowed to cut any book deeply, so as to destroy a good, fair margin. Care must also be taken to cut the margins evenly, at right angles, avoiding any crooked lines. After cutting the book comes "rounding," or giving the back of the book a curved instead of its flat shape. This process is done with the hand, by a hammer, or in a rounding press, with a metallic roller. Before rounding, the back of the book is glued up, that is, receives a coating of melted glue with a glueing brush, to hold the sections together, and render the back firm, and a thorough rubbing of the back with hot glue between the sections gives strength to the volume. Next comes the treatment of the edges of the book, hitherto all white, in order to protect them from showing soil in long use. Sometimes (and this is the cheaper process) the books are simply sprinkled at the edges with a brush dipped in a dark fluid made of burnt umber or red ochre, and shaken with a quick concussion near the edges until they receive a sprinkle of color from the brush. Other books receive what is called a solid color on the edges, the books being screwed into a press, and the color applied with a sponge or brush.