Parchment became the most common writing material during the early Middle Ages in Europe, where it replaced papyrus until the invention of printing in the 15th century created a strong demand for cheaper, more malleable materials. Parchment is made from the skin of sheep and goats and has considerably more strength and durability than papyrus. (Sometimes the term vellum is used indiscriminately, but vellum refers specifically to the skin of calves, used mainly as a binding material.)

The sheep or goat skin undergoes lengthy processing. The hair and flesh are removed with the aid of lime (acting as a strong alkali), then the skin is stretched on a frame where it is scraped, wet, and stretched again until the fibers become aligned.

The primary difference between leather and parchment is that in the production of leather all the processes are designed to produce a supple skin in which the bundles of fibers slide over one another in a flexible fashion. In the production of parchment the fibers are stretched so that they lie almost parallel to form a hard, rigid sheet. Parchment has great stability and permanence if kept in a dry, stable environment.

Parchment rolls were very common, but the chief value of parchment was its ability to be stitched together in large gatherings to form durable and flexible volumes. The sewing to produce the parchment codices was notably Coptic in style until the fifth to eighth centuries, when it became common to sew the parchment signatures onto thongs or cords with heavy wooden boards to stabilize the shape of the text.

Identification

The characteristic features of parchment, which confirm its animal origin, can usually be recognized under close examination with a hand lens (30x) or a microscope. These features include the hair follicle pattern, veining, natural scars and bruises, and, in certain skins, fat deposits. The follicle pattern may be most pronounced across bony areas of the animal, such as the ribs or spine. Raking, transmitted, and ultraviolet light often help to make these features more prominent.

Analytical testing is also possible. But because it involves destructive testing of a small sample taken from the parchment, it should be done only under the supervision of professional conservators.

Cross-sections of parchment can be examined under the light microscope and with scanning electron microscopy. During visual examination it can be difficult to distinguish between certain types of parchment (usually thin flesh splits from the 19th and early 20th centuries, sometimes called "forrel") and highly calendared papers, often called "parchment" paper or "vellum" paper. Imitation parchment made from vegetable matter or paperlike material usually is easily recognizable because the surface characteristics are too even and do not bear the marks of an animal skin.

Condition Concerns

Parchment is hygroscopic (absorbs moisture) and, while chemically stable, is dimensionally unstable and reactive to changes in the moisture level. Because parchment was created by stretching the fibers under strain, moisture will allow the fibers to change shape and cause distortion and wrinkles. Parchment documents need to be kept under some pressure constraint, and bindings in parchment need to be boxed.

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