Vellum. Vellum is prepared animal skin or membrane, typically used as writing material. It is often distinguished from parchment, either by being made from calfskin, or simply by being of a higher quality. Vellum is prepared for writing and printing on single pages, scrolls, and codices. Modern scholars and experts often prefer to use the broader term membrane, which avoids the need to draw a distinction between vellum and parchment. It may be very hard to determine the animal species involved without detailed scientific analysis. Vellum is generally smooth and durable, but there are great variations in its texture which are affected by the way it is made and the quality of the skin. The making involves the cleaning, bleaching, stretching on a frame, and scraping of the skin with a crescent-shaped knife. To create tension, the process goes back and forth between scraping, wetting and drying. Scratching the surface with pumice, and treating with lime or chalk to make it suitable for writing or printing ink can create a final look. Modern paper vellum is made of synthetic plant material, and gets its name from its similar usage and high quality. It is used for a variety of purposes including tracing, technical drawings, plans and blueprints. Quran from the 7th century written on vellum The word vellum is borrowed from Old French velin 'calfskin', derived in turn from the Latin word vitulinum made from calf. However, in Europe, from Roman times, the word was used for the best quality of prepared skin, regardless of the animal from which the hide was obtained. Calf, sheep, and goat were all commonly used, and other animals, including pig, deer, donkey, horse, or camel were used on occasion. 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. However, there has long been much blurring of the boundaries between these terms. In 1519, William Horman could write in his Vulgaria: That stouffe that we wrytte upon, and is made of beestis skynnes, is somtyme called parchement, somtyme velem, somtyme abortyve, somtyme membraan. Writing in 1936, Lee Ustick explained that: To-day the distinction, among collectors of manuscripts, is that vellum is a highly refined form of skin, parchment a cruder form, usually thick, harsh, less highly polished than vellum, but with no distinction between skin of calf, or sheep, or of goat. 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. A portolan chart by Jacobo Russo of Messina Vellum allows some light to pass through it. It is made from the skin of a young animal. The skin is washed with water and lime, and then soaked in lime for several days to soften and remove the hair. Once clear, the two sides of the skin are distinct: the body side and the hairy side. The inside body side of the skin is usually the lighter and more refined of the two. The hair follicles may be visible on the outer side, together with any scars from when the animal was alive. The membrane can also show the pattern of the animal's vein network called the veining of the sheet. The makers remove any remaining hair and dry the skin by attaching it to a frame. They attach the skin at points around the edge with cords and wrap the part next to these points around a pebble. They then use a crescent shaped knife, to clean off any remaining hairs. The makers thoroughly clean the skin and process it into sheets once it is completely dry. They can extract many sheets from the piece of skin. The number of sheets depends on the size of the skin and the required length and breadth of each individual sheet. For example, the average calfskin could provide roughly three and a half medium sheets of writing material. The makers can double it when they fold the skin into two conjoined 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 makers rubbed them with a round, flat object to ensure that the ink would adhere to the surface. Even so, ink would gradually flake off of the membrane, especially if it was used in a scroll that was frequently rolled and unrolled.