13.The medieval Mappa Mundi in England's Hereford cathedral, for example, is little more than drawings on vellum, or stretched calfskin, and it lacks Ptolemy's geometric method.
15.Your initial reaction, you see a drawing on ink coloured chalks, but also ink washes on vellum, the initial reaction of course is Leonardo didn't do that.
16.And I wondered if because there's no other works that we know of which Leonardo worked on vellum, it made a difference in terms of attribution according to technique?
17.He talks about Jean's box of pigments, he talks about how do you get double and single sheets which is cutting vellum out of a irregular shaped skin.
18.The early Christian missionaries introduced the more rounded Roman alphabet (much as we use today), which was easier to read and more suited for writing on vellum or parchment.