What is the difference between parchment, vellum, and leather?
As far as parchment and vellum go, the difference is pretty much semantic at this point in history. The roots of the words come from different sources. Parchment arrived in the English language from the German Perkament, which in turn came from Pergamena in Italian (and before that, Pergamena in Latin). We can reach back even further to the word Pergamon, from antiquity, which referred to the city in Asia Minor where the material was first recorded as being mass produced. These days, parchment in general refers to any type of animal skin turned into a paper-like material from physical action, including the removal of extraneous flesh, fat, and hair.
Meanwhile, vellum comes from the Old French word Velin, which means calfskin. Historically speaking, calfskin has been the finest parchment available, so people have long referred to refined parchment as vellum. Here’s a simple formula: All vellum is parchment, but not all parchment is vellum.
Leather refers to the same raw material — animal skin — that has been chemically altered to render it impervious to rot. There are many ways to tan a skin, and the resultant leather will vary in characteristics, but it will always stand up to moisture, heat, and mechanical action better than any untanned/raw skin.