Fig. 28.—Faulty sewing over a band.
Now comes an interesting point, and that is the exact way in which the threads are passed over the bands. We will first see that if the thread is drawn through the back fold of the section, round a hand and back again through another hole, that there is a weak construction, inasmuch as the thread will have a strong tendency to cut through the paper at a and b, because there is in each case a side strain. It therefore seemed necessary that the thread should make its return journey by the same hole through which it emerged, but if simply done, this did not mend matters much, as the strain still tended to pull this hole open wider. A line of exit and entrance without any side pull was needed, and this was found by means of a very clever device. A broad band of leather or vellum was cut through lengthways, leaving a solid piece at each end.
Fig. 29.—Mediæval sewing round double band.
Now when the sewer came to this band he ran the thread straight through the slot, then brought it round the entire band, under it, between it and the back of the book, and down again, back through the slot, and in at the same point from which it emerged. The result of this is that there is no strain at all on the needle hole through which the thread passes, as the pull is quite straight both coming and going. This is undoubtedly the best form of sewing a book on bands, and a book so treated is said to be sewn on “double bands.” But our recent work is not always true, although from the outside it appears correct, because in numbers of cases such double bands are simply glued on the outside of the back, the real sewing, of a very inferior kind, possibly even done by machinery, being hidden underneath the leather. Few great binders except Charles Lewis have ever used sham bands.
Flexible sewn books can be had now if wanted, but the sewing on the bands is not quite the same as the fine mediæval double bands I have described. It is, however, practically nearly as good, and the bands themselves can be made smaller.
Fig. 30.—Modern sewing round single band.
The modern method is to bring the needle and thread through the back of the section as usual, then give it one turn onwards over the band and back again through the same hole. It will be seen that this is a thoroughly sound principle, and brings no strain upon the back of the section.