Exploring

Inherent Vice: Materials

Parchment and Vellum

The invention of parchment is often credited to King Eumenes of Pergamum, an ancient city in Asia Minor, in the second century BC, but writing on animal skins was common for centuries before that. The term parchment sometimes refers to any skin that has been prepared for writing, and sometimes refers specifically to sheepskin. The term vellum refers to calfskin only. Parchment and vellum were originally used for scrolls and other documents. They were also used as pages in books from the second century AD onward, and as bookbinding material.

Until the fourth century AD, skins were treated with salt, flour, and other vegetable products to prepare them for writing; after this, skins were treated with lime water, an alkaline substance. Parchment is generally more alkaline and more stable than leather.

This parchment object was stored poorly and has become dirty and cockled.

Characteristic Types of Deterioration

Beginning in the early 19th century, chemicals (such as sulphur compounds) were added to the lime water baths to speed up the process of preparing the skin, but these made the skin weaker. Additional chemicals such as formaldehyde were then added to try to counteract this weakness, but only resulted in stiffer skins with less elasticity. In addition, sulphur compounds remained in the skin after rinsing and were converted into sulphuric acid, which in turn reacted with calcium carbonate to produce gypsum. The presence of gypsum causes parchment to turn a gray color.

Parchment is also subject to photochemical reactions (the result of light exposure) in which hydrogen peroxide forms, causing the parchment to break down and become brittle and fragile (gelatinized). If gelatinized parchment is brought into contact with water, it will disintegrate into loose flakes.

See Overview of leather and parchment manufacture and Causes and phenomena of leather and parchment decay, both published online by the National Library of the Netherlands for a more detailed description of parchment manufacture and parchment deterioration.