Sometimes it is thought necessary to fill up worm-holes in the paper. This may be done by boiling down some paper in size until it is of a pulpy consistency, and a little of this filled into the worm-holes will re-make the paper in those places. It is a very tedious operation, and seldom worth doing.
Mending vellum is done in much the same way as mending paper, excepting that a little greater overlap must be left. It is well to put a stitch of silk at each end of a vellum patch, as you cannot depend on paste alone holding vellum securely. The overlapping edges must be well roughed up with a knife to make sure that the paste will stick. A cut in a vellum page is best mended with fine silk with a lacing stitch (see fig. 18).
Mending is most easily done on a sheet of plate-glass, of which the edges and corners have been rubbed down.
If an old book that has had much wear is examined, it will generally be found that the leaves at the beginning and the end have suffered more than the rest of the book. On this ground, and also to enable people who must write notes in books to do so with the least injury to the book, it is advisable to put a good number of blank papers at each end. As these papers are part of the binding, and have an important protective function to perform, they should be of good quality. At all times difficulty has been found in preventing the first and last section of the book, whether end papers or not, from dragging away when the cover is opened, and various devices have been tried to overcome this defect. In the fifteenth century strips of vellum (usually cut from manuscripts) were pasted on to the back of the book and on the inside of the boards, or in some cases were merely folded round the first and last section and pasted on to the covers. The modern, and far less efficient, practice is to "overcast" the first and last sections. This is objectionable, because it prevents the leaves from opening right to the back, and it fails in the object aimed at, by merely transferring the strain to the back of the overcast section.
In order to make provision for any strain there may be in opening the cover, it is better to adopt some such arrangement as shown in fig. 19. In this end paper the zigzag opens slightly in response to any strain.