Before paper was introduced to Europe
books were written on specially prepared animal skins, vellum or parchment.
Handwritten books on paper became more common during the 15th century
before the invention of printing, but vellum continued to be used.
Vellum was also used for printed books. Because it was thought to
last longer it was quite often used for schoolbooks. Vellum was more
expensive so it was also used for more luxurious copies.
There are 48 copies of the Gutenberg Bible still in existence,
not all of them complete, some being only substantial fragments
of one of the two volumes. Of these, 12 are printed on vellum, in
this case calf's skin. The Grenville copy of the Gutenberg Bible
is printed on vellum.
Detail of folio 120 verso of vol.1 of the vellum copy. The skin has been repaired with needle and thread. Larger image
You can see how much more uneven the surface is. If the skin got
damaged during preparation it could simply be sown together again.
The skin of about 170 calves would have been required for each
copy of the Bible printed on vellum.