Parchment Museum

Christopher Clarkson, "Rediscovering Parchment: The Nature of the Beast."  The Paper Conservator.  16 (1992) 5-16.  Online link (pay-per-view from Taylor and Francis).

1)  Though animal skins had been used for centuries as a durable substrate for writing and painting, mass produced and finely finished parchment originated in Pergamum after the Egyptian emperor cut off Pergamum's source of papyrus around 200 BCE in order to strengthen the power of the great library of Alexandria (according to Pliny's Natural History XIII.11).  The medieval Latin name for parchment was
pergamenum.  Spreading rapidly to Europe, parchment manuscripts coincided with the rise of Christianity and they were used to make the earliest surviving Christian biblical codices (Codex Vaticanus, Codex Sinaiticus, Codex Alexandrinus, and Codex Ephraemi Rescriptus, circa 325-450 CE).

2)  Parchment can be made from almost any untanned animal hide that has been properly fleshed and de-haired, stretched and dried and smoothed.  The most common hides encountered in surviving medieval MSS are calf, sheep, goat, and pig (Christina Duffy, "Here's Looking at You Kid: Under the Microscope with Leather," British Library Collection Care Blog, October 30, 2013).
Also see "Leather Identification," Lili's Bookbinding Blog, January 19, 2009.

3)  Parchment is humidity-sensitive: 55-65% humidity is ideal.  Lower humidity causes parchment bindings to crack and boards to detach.  Higher humidity causes parchment leaves to curl until books cannot be closed.

4)  Parchment, like paper, can be called a "support" or "substrate" because it exists to support ink or painted pigments.  When parchment is deformed by fluctuations in humidity, ink and pigments can be distorted or sloughed off entirely.

5)  Parhment does not want to lie flat, even in ideal humidity conditions.  Scribes worked with a knife in one hand and a pen in the other, using the former to control the parchment (and to "erase" errors by scraping off the ink), and the latter to form the letters.

https://medievalfragments.files.wordpress.com/2013/10/lawrence_of_durham.jpg
Lawrence of Durham, Durham, University Library. Ms. Cosin V.III. 1. f. 22v. from Irene O'Daly, "Writing the Word: Images of the Medieval Scribe at Work," Medieval Fragments [U. Leiden Blog, ] 10/13/14. https://medievalfragments.wordpress.com/2013/10/18/writing-the-word-images-of-the-medieval-scribe-at-work/ 

Key Parchment Features and their Terms of Art
Hair vs. flesh side--rougher grain/smoother grain and darker/lighter (Figs. 16, 17 and see 25, 26 for matching openings hair-hair, flesh-flesh)
Flesh wounds, sewing and demilune scars or "flaymarks" (Figs. 3, 4, 5, 15, 20, 22, 23, 29, 32, 33, 34, 35a-b, 36-39a-b).
Artery, vein and trapped blood traces (Figs. 6 & 14).
Flank, spine, and pelvis traces; neck rings; leg gaps (Figs. 7, 8, 9, 10, 111, 12).
Parchmentiers' ID marks--intentional codes to identify maker (cf. papermakers' watermarks and countermarks) (Figs. 18a-b, 19).
Grain-split skins (often mistakenly called "uterine vellum" (Fig. 27a-b, 28, 30.
Pigment and iron-gall ink corrosion of parchment substrate (Fig. 41, 42).
Post-production damage due to spiders, mold, rodents, burns, sneezes, hot wax, and cat pee  (Figs. 2 & 43-54a-b).