In Europe, from Roman times, the term vellum was used for the best quality of prepared skin, regardless of the animal from which the hide was obtained, calf, sheep, and goat all being commonly used (other animals, including pig, deer, donkey, horse, or camel have been used). Although the term derives from the French for "calf", except for Muslim or Jewish use, animal vellum can include hide from virtually any other mammal. The best quality, "uterine vellum", was said to be made from the skins of stillborn or unborn animals, although the term was also applied to fine quality skins made from young animals. Many libraries and museums increasingly use only the safe if confusing term "membrane"; depending on factors such as the method of preparation it may be very hard to determine the animal involved without using a laboratory, and the term avoids the need to distinguish between vellum and parchment.
French sources, closer to the original etymology, tend to define velin as from calf only, while the British Standards Institution defines parchment as made from the split skin of several species, and vellum from the unsplit skin. In the usage of modern practitioners of the artistic crafts of writing, illuminating, lettering, and bookbinding, "vellum" is normally reserved for calfskin, while any other skin is called "parchment".
Vellum is a translucent material produced from the skin, often split, of a young animal. The skin is washed with water and lime (Calcium hydroxide), but not together. It is then soaked in lime for several days to soften and remove the hair. Once clear, the two sides of the skin are distinct: the side facing inside the animal and the hair side. The “inside body side” of the skin is the usually lighter and more refined of the two. The hair follicles may be visible on the outer side, together with any scarring, made while the animal was alive. The membrane can also show the pattern of the animal's vein network called the “veining” of the sheet.
Any remaining hair is removed (“scudding”) and the skin is dried by attaching it to a frame (a “herse”). The skin is attached at points around the circumference with cords; to prevent tearing, the maker wraps the area of the skin to which the cord is to be attached around a pebble (a “pippin”). The maker then uses a crescent shaped knife, (a “lunarium” or “lunellum”), to clean off any remaining hairs. Once the skin is completely dry, it is thoroughly cleaned and processed into sheets. The number of sheets extracted from the piece of skin depends on the size of the skin and the given dimensions requested by the order. For example, the average calfskin can provide three and half medium sheets of writing material. This can be doubled when it is folded into two conjoint leaves, also known as a bifolium. Historians have found evidence of manuscripts where the scribe wrote down the medieval instructions now followed by modern membrane makers. The membrane is then rubbed with a round, flat object (“pouncing”) to ensure that the ink would adhere well.
Once the vellum is prepared, traditionally a “quire” is formed of group of several sheets. Raymond Clemens and Timothy Graham point out, in "Introduction to Manuscript Studies", that “the quire was the scribe’s basic writing unit throughout the Middle Ages”. Guidelines are then made on the membrane. They note “'pricking' is the process of making holes in a sheet of parchment (or membrane) in preparation of it ruling. The lines were then made by ruling between the prick marks...The process of entering ruled lines on the page to serve as a guide for entering text. Most manuscripts were ruled with horizontal lines that served as the baselines on which the text was entered and with vertical bounding lines that marked the boundaries of the columns.”
Most of the finer sort of medieval manuscripts, whether illuminated or not, were written on vellum. Some Gandharan Buddhist texts were written on vellum, and all Sifrei Torah (Hebrew: ספר תורה ; plural: ספרי תורה, Sifrei Torah) are written on kosher klaf or vellum.
A quarter of the 180 copy edition of Johannes Gutenberg's first Bible printed in 1455 with movable type was also printed on vellum, presumably because his market expected this for a high-quality book. Paper was used for most book-printing, as it was cheaper and easier to process through a printing press and bind.
In art, vellum was used for paintings, especially if they needed to be sent long distances, before canvas became widely used in about 1500, and continued to be used for drawings, and watercolours. Old master prints were sometimes printed on vellum, especially for presentation copies, until at least the seventeenth century.
Limp vellum or limp-parchment bindings were used frequently in the 16th and 17th centuries, and were sometimes gilt but were also often not embellished. In later centuries vellum has been more commonly used like leather, that is, as the covering for stiff board bindings. Vellum can be stained virtually any color but seldom is, as a great part of its beauty and appeal rests in its faint grain and hair markings, as well as its warmth and simplicity.
Lasting in excess of 1,000 years—Gregory the Great, Pastoral Care for example dates from about 600 and is in excellent condition—animal vellum can be far more durable than paper. For this reason, many important documents are written on animal vellum, such as diplomas. Referring to a diploma as a "sheepskin" alludes to the time when diplomas were written on vellum made from animal hides.