The first operation in bookbinding is folding the printed sheets, and it requires great care if the book is to have a good appearance when bound. It is usual for printers to leave more margins to the outsides of the sheet, so that when the sheets have been folded the margin will be broader at the foreedge and tail than at the head and back. The head and back are always at the fold, the tail and foreedge being towards the outside of the sheet. If, the paper presents any little difference in size, the: two latter edges being cut first in the process of binding, the difference will then be taken off, and the margin will be the same all round.

The plan adopted is to fold to the pages of print, and not to the edge of the paper, for the least variation in the size of the sheet would result in a spoiled book.

Papers are made in various sizes, and are known by the following terms: Imperial (30 in. by 22 in.), royal (25 in. by 20 in.), demy (22 ½ in. by 17 ½ in.), crown (20 in. by 15 in.), foolscap (17 in. by 13 ½ in.), and pott (15 in. by 12 ½ in.); and the sizes of books are denominated according to the number of leave" into which the sheet is folded. The ordinary sizes are folio, 4to, 8vo, 12mo, 16mo, 24mo, and 32 mo. A sheet, when folded, has twice as many pages as leaves, for the obvious reason that it is printed on both sides. In speaking of the size of The Quiver, for example, it is said to be royal octavo (8vo), because the sheet has been folded to one-eighth its original size, and has sixteen pages. The octavo is the most general size of a book, and the type matter is so imposed that, when the sheet is folded, the sixteen pages will follow consecutively.

In the early days of printing only a few pages could be printed at one operation. Now, however, the number of pages that can be printed on one sheet of paper is only limited by the size of the printing machine. But, as a matter of convenience, the sheets the binder has to deal with usually con­sist of 4, 8, 16, 32, 64, or 128 pages, the number of pages that are folded into one sheet depending on the price at which the book is to be sold. In the best work, the sheets do not contain more than sixteen pages that is, eight pages on each side of a sheet of paper; and each sixteen pages is called a section or sheet. At the bottom of one of the pages (the first numerically) of each sheet is printed a letter or figure, known as the signature; this is the guide when folding, and, as the letters or figures follow each other consecutively, the placing of the sheets in their proper order when sewing them is thus ensured. Thus, when the sheets in a work each consist of sixteen pages, the signatures­ will be found at the foot of pp. 1, 17, 33, 49, etc. The manner of folding is as follows: A printed sheet (say, pp. 1 to 16) is laid on a table in front of the operator, that side of the sheet containing p. 1 (the signature side) lying in contact with the table. Page 2 backs p. 1, and p. 2 should be the corner page close to the operator's left-hand (see Fig. 28). The corner page at the folder's right hand is p. 3. The object to be obtained is to fold the sheet over in such a way as to place the figure 3 exactly on the top of the figure 2. If this is properly done, the printed lines on p. 3 will lie exactly on the printed lines on p. 2, line for line, and when the book is bound the white margins round the print on each page will all be of the same relative widths, the front and the bottom margins being always wider than the top and the inside margins. The result of the first fold is shown by Fig. 29. The second fold brings pp. 5 and 12 over on to pp. 4 and 13; the result of this fold is shown by Fig. 30. The third fold brings p. 9 on to p. 8, the folded sheet is turned over, and the result seen by Fig. 31. The first page is p. 1, containing the signature, in this case the letter A, and the last page of the sheet is p. 16. All folding operations follow this general plan of doubling over the sheet for each fold; to this rule there are, of course, a few exceptions, but these are easily recognized. Before beginning to fold, the folder should ascertain how many pages are contained in a section. To every section belongs a distinguishing signature or letter, and all the pages coming between the first page of, say, signature A and the first page of signature B belong to signature A. Thus it may happen that signature A consists of thirty-two pages; but in order to ensure better folding, the thirty two pages are printed so as to fold in two sections, one of which is inserted in the centre of the other. The pages and signatures are then arranged as follows: The outer sheet contains pp. 1 (signature A) to 8 and pp. 25 to 32; the inner sheet, called the inset, contains pp. 9 (signature A *) to 24. The sheet and its inset are folded independently of each other in the manner already described, and when the inset is inserted p. 9 follows p. 8, and p. 25 follows p. 24. This is the general rule applicable to all insets of this character. Exceptions to this rule may, of course, occur, but these exceptions would probably be caused by the limited plant of the printer who produced the book. A sheet may consist of several insets, but the signatures would follow the rule already stated. The worker must be always on the lookout for things of this kind. Figures as well as letters are used as signature marks; where letters are used, the first sheet of the book (excluding the title and contents) sometimes begins with B instead of A, and the letters J and v are not used in all cases. The folder is held in the right hand, and is used for smoothing the folds, etc. Creasing and puckering of the folds must be guarded against; these mishaps readily occur if the folder is not properly used.

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