From Wiki: Parchment is a material made from animal skin; often calfskin, sheepskin, or goatskin. Its most common use was as a material for writing on, for documents, notes, or the pages of a book, codex or manuscript. Parchment is limed, scraped and dried under tension. It is not tanned; therefore, it is very reactive to changes in relative humidity and will revert to rawhide if overly wet.
While the term parchment refers to any animal skin, particularly goat, sheep, or cow, that has been scraped or dried under tension, vellum refers exclusively to calfskin.
The heyday of parchment use was during medieval times, but there has been a growing revival of its use among artists since the late 20th century. Although parchment never stopped being used (primarily for governmental documents and diplomas) it had ceased to be a primary choice for artist’s supports by the end of 15th century Renaissance. This was partly due to its expense and partly due to its unusual working properties. Parchment consists mostly of collagen. When the water in paint media touches parchment’s surface, the collagen melts slightly, forming a raised bed for the paint, a quality highly prized by some artists.