4.—The right hand creases from top to bottom.
5.—Left hand turns sheet over to other side, both hands take hold as before, nip together last fold, and adjust pages and fold.
6.—Crease from top to bottom, laying aside sheet to left, fold lying to right.
The whole process, which demands considerable dexterity, is only to be thoroughly learned by example and imitation; but study the illustrations, which are correctly drawn from life.
This is the way sheets are folded when they come direct from the press; but if they had already been folded in quires, as is usually the case with school and hymn books, the sheets would simply be folded in the middle for convenience of storage and despatch.
In this case the quires must first be opened, the crease taken out, and the sheets laid open. This work is called "breaking the backs." The unfolded sheets are folded in exactly the same manner, but before the last crease the sheet is turned, creased from bottom to top, and put aside in such a way that the sheet is turned over, that is face downwards. If this precaution is not observed, the folded sheets would afterwards be found in wrong order.
At this point we might remark that the top, both of the book and the single page, is called the head, the bottom the tail. These commonly used terms will very frequently crop up.
The folding of a 4to sheet is exactly the same, excepting that the last fold is omitted; the second signature lies face upwards at top on the right, the first signature lies downwards at top left hand.
Folios are made up but rarely nowadays, except in artistic éditions de luxe, Bibles, and missals; they are simply folded in the middle; the signatures appear as in 8vo format.
Duodecimo format, that is, a sheet printed to make 12 pages on each side, is so printed that the third part of the sheet has to be cut off with a knife or machine. This work is done in various ways: the sheet may be folded without regard to the one-sided elongation; after folding the part is cut off with a knife or machine at the proper place and the detached portion inserted in the middle of the main section; the small section is therefore called "the inset." On the other hand, the inset may be cut off before folding and then separately folded and inserted. This is the more usual method.