They used to make high end books out of vellum, described as “the semi-transparent inner membrane of calf skin,” or the even finer uterine vellum, that membrane taken from the skin of embryonic or still-born calves. Marc Epstein tells is that these materials were better suited than paper for absorbing the pigments and gold leaf used to illuminate deluxe medieval manuscripts. The skin-membranes are both tough and soft (Marc Epstein Skies of Parchment, Seas of Ink: Jewish Illuminated Manuscripts, p.30).