Impositions and Folding Schemes
The diagrams show different impositions (the way a forme is laid down so as to give a particular arrangment of pages) and folding schemes (the way a sheet so printed is folded into signatures): cf. pp. 160 sqq. The examples given are not exhaustive: particularly for the more complicated impositions a number of further variants are possible which were, and still are, practised.
Though consecutive numbering of pages was already an established practice in Plantin's day, the earlier system of signatures was still in use and remained so for at least two more centuries. Signatures in old books are usually more accurate and trustworthy than page numbers: the latter are often full of errors. (According to one theory, paging was a job often entrusted to apprentices.) The basic system of signatures is as follows: each ‘folding element’ or ‘unit’ of four pages shows a signature on the first page. Thus a normal octavo sheet (16 pages folded together in 4-page units) will show signatures A, A2, A3, A4 on pp. 1, 3, 5, and 7 respectively. No signatures appear on pp. 9, 11, 13, 15, but on p. 17 signature B will be found, and B2, B3, and B4 on pp. 19, 21, 23, and so on. In the following diagrams both folios and signatures are shown; this will be found particularly useful in the more complicated schemes, where one sheet will produce for instance A, A2, A3, A4, followed by B and B2 (in other words, 24 pages folded and sewn into 16 and 8).
The reader should bear in mind that in diagrams representing formes all lettering appears in reverse; those representing printed pages show numbers the right way round. Odd-numbered (recto) pages read from the gutter (inside margin) towards the fore-edge; even-numbered (verso) pages read towards the gutter.
Fig. 1. Folio imposition. Folding scheme in fig. 14 on p. 540.
Fig. 2. Normal quarto imposition. Folding scheme in fig. 15 on p. 541.
Fig. 3. Quarto imposition for work and turn operation (cf. p. 304). This imposition is still the usual one for 4-page folders. To produce a run of 1,000 copies the pressman takes 500 sheets which are printed on one side to begin with. The stack is then turned and the blank side printed from the same forme; as a result p. 1 thus backs p. 2, and p. 3 backs p. 4. Finally the sheets are cut in half, thus producing 1,000 half sheets printed both sides with the correct pages. Folding scheme in fig. 16 on pp. 542-543.
Fig. 4. Normal octavo imposition. This imposition is still the usual one for book-work printed on relatively small presses. See also figs. 11 and 24 on pp. 537 and 558. Folding scheme shown in fig. 17 on pp. 544-545.
Fig. 5. Octavo imposition for work and turn operation: Plantin's ‘impression à demi-feuilles’. The principle is the same as described under fig. 3 on p. 529. For formes with a greater number of pages (cf. figs. 11 and 12 on pp. 537 and 538) there is an additional advantage. When the normal imposition (fig. 4) is practised, the pressman cannot start printing before 16 consecutive pages are composed and passed for press (p. 1 and p. 16 are in the same forme); in the work and turn operation, however, the pressman can start his job as soon as 8 pages are composed and approved. Thus the flow of work from composing room to pressroom is more regular with less unproductive waiting about. Printers find this useful for rush jobs. Folding scheme in fig. 18 on pp. 546-547.
Fig. 6. One of several possible 12mo impositions. Folding scheme in fig. 19 on pp. 548-549.
Fig. 7. Another 12mo imposition. Folding scheme in fig. 20 on pp. 550-551.
Fig. 8. A variant of the 12mo impression shown in fig. 7. Folding scheme in fig. 21 on pp. 552-553.
Fig. 9. A 12mo imposition for work and turn operation. Folding scheme in fig. 22 on pp. 554-555. The rather intricate 12mo fell into disuse with the advance of mechanized binding, as folding machinery is not usually adapted to performing such complicated tasks. In modern printing these impositions may be used when a book of a certain format must be printed on available paper of awkward size.
Fig. 10. Normal 16mo imposition. Folding scheme in fig. 23 on PP-556-557.
Fig. 11. A 16mo imposition for work and turn operation. Folding scheme in fig. 24 on pp. 558. This imposition is often used in modern printing, but was much less used in the time of Plantin and the Moretuses, except for small books. Presses could only be built to a certain maximum size, as the printing of larger formes would have made too much of a demand on the muscular strength of the pressman. This limitation of size was only overcome with the development of modern power-driven cylinder presses. Paper sizes were also limited for much the same reasons before the advent of machine-made paper.
Fig. 12. An 18mo imposition, basically devised for work and turn operation. It should be noted, however, that for backing up the sheet pp. 7, 8, 11, and 12 must be arranged differently. Folding scheme in fig. 25 on p. 559.
Fig. 13. An 18mo imposition devised in an inner and an outer forme. Folding scheme in fig. 26 on pp. 560-561. These impositions were not very common, most probably because of the highly intricate way of folding the sheets. Use of the imposition shown in fig. 12 in fact would mean that a loose leaf (A5, containing pp. 9 & 10) had to be pasted into the centre of the folded sheet.
Fig. 14. A folio sheet: flat (both sides) and folded. Cf. fig. 1 on p. 527.
Fig. 15. A quarto sheet printed according to the imposition shown in fig. 2 on p. 528.
Fig. 16. A quarto sheet printed in work and turn operation according to the imposition shown in fig. 3 on p. 529. The sheet is first cut in half, thus producing two identical 4-page flat sheets (opposite left). After having been folded again two identical signatures result, with pp. 1 and 4 at the outside and pp. 2 and 3 at the inside (opposite right).
Fig. 17. An octavo sheet printed on both sides (opposite page) according to the imposition shown in fig. 4 on p. 530. On this page, left, the first fold; at bottom left, the second fold: at bottom right, the third (and final) fold. Usually when folding by hand the top edge is slightly cut between pages 12 and 13 after the second fold (at the top left hand corner of the diagram) so that the air may escape. In folding machines the second fold is perforated, in one operation, for the same purpose.
Fig. 18. An octavo sheet printed in work and turn operation as shown in fig. 5 on p. 531. The sheet is first cut in half (opposite page, top) resulting in two identical flat sheets of 8 pages. These are then folded twice as if they were quarto sheets. Cf. fig. 15 on p. 541.
Fig. 19. A 12mo sheet printed according to the imposition shown in fig. 6 on p. 532. After being printed at both sides the sheet is cut (along the heavy lines) into three strips each containing 8 pages (as shown at left). These strips are then folded in parallel (the first fold is shown for two strips only) and finally inserted into each other. The signatures (A, A2, A3, A4, A5, A6) are a great help to the binder in this kind of operation.
Fig. 20. A 12mo sheet printed according to the imposition shown in fig. 7 on p. 533. The sheet is really built up as two signatures: one ordinary octavo containing pp. 1-16 (A, A2, A3, A4) and a strip of 8 pages (pp. 17-24; B, B2). The former is treated as shown in fig. 17 on pp. 544-545, the latter as the innermost 8-page strip (A5, A6) shown in fig. 19 on p. 549.
Fig. 21. A 12mo sheet printed according to the imposition shown in fig. 8 on p. 534. The lay-down of this forme is basically similar to the one shown in figs. 8 and 20. They differ in that the folded sheet of 16 pages is inset into the folded strip of 8 pages. Thus the 16-page signature contains pp. 5-20 (A3, A4, A5, A6) and the 8-page strip pp. 1-4 and 21-24. The latter is identical to the outer strip shown in fig. 19.
Fig. 22. A 12mo sheet printed according to the imposition shown in fig. 9 on p. 535 for work and turn operation. The same pages are printed on both sides of the paper. The printed sheet is cut twice along the heavy lines and produces one signature of 8 pages (pp. 1-4 and 9-12) twice and one signature of 4 pages (pp. 5-8), also twice. Both are folded and the 4-page signature (A3) inserted into the 8-page signature (A, A2). Most binders prefer to insert into the 4-page signature as it is easier to avoid mistakes in this way.
Fig. 23. A 16mo sheet printed according to the imposition shown in fig. 10 on p. 536. The sheet is folded four times, each fold crosswise to the previous one. Exact folding of such sheets is difficult, as much air tends to be caught in the folds. Usually this system was only used for small books printed on thin paper. Cf. fig. 17
Fig. 24. A 16mo sheet printed according to the imposition shown in fig. 11 on p. 537 for work and turn operation. The sheet is cut in half along the heavy line, resulting in two identical signatures of 16 pages which are folded as shown in fig. 17 on p. 545.
Fig. 25. An 18mo sheet printed according to the imposition shown in fig. 12 on p. 538, cut into its eight components. The numbered arrows indicate cuts in their consecutive order. As this imposition is basically a work and turn operation, each component appears twice. Folding is done along the dotted lines: the finished signature consists of an 8-page component (A, A2 containing pp. 1-4 and 15-18), two 4-page components inserted (A3: pp. 5-6 and 13-14, and A4: pp. 7-8 and 11-12). Finally the single leaf A5 (pp. 9 and 10) is pasted into the centre of the folded signature.
Fig. 26. An 18mo sheet printed according to the imposition shown in fig. 13 on p. 539. The flat sheet (both sides of which are shown opposite) is first cut into four pieces along the heavy lines. The resulting components are folded according to schemes appearing in previous figures. First, an octavo folding A, A2, A3, A4 containing pages 1-8 and 11-20, into which the component A5 (pp. 9-12) is inserted. The component B, B2 is folded twice, crosswise, and contains pp. 21-24 and 33-36, into which the element B3, B4 (pp. 25-32) is inserted after parallel folding. Numbers between brackets indicate the pages backing those visible.