The sections are then taken, one by one, placed face downwards in a frame, and sewn through the back by a continuous thread running backwards and forwards along the backs of the sections to upright strings fastened at regular intervals in the sewing frame. This process unites the sections to one another in series one after the other, and permits the perusal of the book by the simple turning of leaf after leaf upon the hinge formed by the thread and the back of the section.
A volume, or series of sections, so treated, the ends of the string being properly secured, is essentially "bound"; all that is subsequently done is done for the protection or for the decoration of the volume or of its cover.
The sides of a volume are protected by millboards, called shortly "boards." The boards themselves and the back are protected by a cover of leather, vellum, silk, linen, or paper, wholly or in part. The edges of the volume are protected by the projection of the boards beyond them at top, bottom, and fore-edge, and usually by being cut smooth and gilt.
A volume so bound and protected may be decorated by tooling or otherwise upon all the exposed surfaces (upon the edges, the sides, and the back) and may be designated by lettering upon the back or the sides.
The degree in which a bound book is protected and decorated will determine the class to which the binding will belong.
(1) In cloth binding, the cover, called a "case," is made apart from the book, and is attached as a whole after the book is sewn.
(2) In half binding, the cover is built up for and on each individual book, but the boards of which it is composed are only partly covered with the leather or other material which covers the back.
(3) In whole binding, the boards are wholly covered with leather or other durable material, which in half binding covers only a portion of them.
(4) In extra binding, whole binding is advanced a stage higher by decoration. Of course in the various stages the details vary commensurately with the stage itself, being more or less elaborate as the stage is higher or lower in the scale.
The process of extra binding set out in more detail is as follows:—