Goatskin leather has a characteristic follicle pattern consisting of rows of hair pores, sometimes predominantly parallel and lying in the grooves of the grain. The grain exhibits numerous variations. Terms best avoided: Turkish leather, morocco, shagreen, and saffian.
As a rule sheepskin leather - notably that of wool sheep, rather than hair sheep - has a smoother surface and a less pronounced grain than goatskin; the hair pores are arranged in groups rather than rows. Sheepskin makes an inferior covering material: the removal of the high amount of fat (up to 30 %) during manufacture gives it a loose structure. Moreover, the upper layer is weak and easily damaged (chafed). Sheepskin is often impressed with an artificial grain (especially in the nineteenth century after being finished with water- and solvent-based finishes - editorial note) in imitation of better/more expensive kinds of leather.
Alum-tawed, red-dyed sheepskin is often used for binding purposes. Basan is a vegetable-tanned, natural sheepskin (its beige colour comes from the tanning).
Calfskin has a smooth surface and a very dense and random follicle pattern. Alt-hough usually vegetable-tanned it is occasionally alum-tawed. It is often dyed, sprinkled and so forth. Cowhide is too thick to be used for covering material, but has been used for straps and (usually alum-tawed) for bands.
The leather of young cattle, tanned with willow bark and impregnated with birch tar oil is called Russia leather. In most cases it is finished with an artificially applied check pattern.
Pigskin has a characteristic follicle pattern made up of groups of three and visible to the naked eye, and a not particularly pronounced grain. It is usually alum-tawed (and has often turned sallow and stiff).
Sealskin comes in fine and coarse grain variants. The follicle pattern is irregular and independent of the grain (hence it is found on the rises as well as in the hollows). There is some resemblance to goatskin and it has an oily feel."
Methods of preparing parchment also can give clues as to animal and the date it was made:
"Parchment was used chiefly for writing, first on a scroll - as is still the case in Israel - and from the second century BC onwards in book form. To make a book, the rectangular cut sheets might be folded one or more times. The skins of sheep and goats from the areas round the Mediterranean were rarely more than 50 cm long by 40 cm wide. In northern regions we find larger skins and also calfskins being used to make books.
The term pergamena is first used in the Edict of Diocletian (301 AD); until that time the term membrana had been used. It is generally accepted that the use of a new term indicates a new or modified product, but so little is known about the parchment of those days that it is impossible to say with any certainty whether this was the case here.
One of our few informants about pre-Christian times is the (unreliable) Roman historian Pliny. He writes that the king of Pergamon (in present-day Turkey), Eumenes II (197-159 BC), was forced to look for alternative writing materials when the import of papyrus from Egypt was suspended. This is supposed to have led to the invention of parchment. Although parchment had been known at least eight hundred years before this date, Pergamon did have a reputation for good quality parchment in classical antiquity. The great change occurred around the 4th century AD, when people started manufacturing parchment using lime water. Until the fourth century skins were mostly treated with salt, flour and other vegetable products that were used to remove the hairs and to prepare the skin. The lime water method may have been introduced by Jews and Arabs to Spain in the early Middle Ages, after which it spread throughout the rest of Europe. Jewish parchment was lightly tanned on the surface with vegetable tannins. Another technique, the splitting of skins, was also known to the Jews and Arabs, even before the Middle Ages. In the West the traditional procedure to obtain the required thickness was to shave the full skin.
Formulas and depictions of parchment manufacturing have come down to us, especially from the late Middle Ages. There is considerable correspondence between these mediaeval formulas and those used by modern parchment makers, and even the processing and tools have not changed fundamentally. For the most part, parchment manufacture is still a matter of handwork.
The definition of parchment used in this publication and taken from Kneep en Binding, states that it is a skin treated with lime water and dried while stretched. This implies that all parchment-like skins that are treated with other substances, such as alum and enzymes, or have been given a surface tanning, or been dried unstretched, cannot properly be called parchment. However, these variants are seldom encountered in bookbinding conservation.
One of the oldest and most detailed descriptions of this lime water method is found in an early 12th-century formula. (Theophilus Presbyter, Schedula diversarium artium. British Museum MS. Harley 3915, fol. 128r.) More modern formulas (i.e. up to the end of last century), indicate how parchment is made 'nowadays'. If we compare the different formulas we find that the oldest does not explain the process whereas modern formula preparations often give very elaborate explanations.
Modern formulas, like those of the twelfth century, begin by soaking the skins in water so as to restore the moisture lost between fleecing and preservation. Soaking swells the skin, thus allowing the lime to penetrate more deeply, and rinses away the salt used as preservative.
In the twelfth century the skins were then put into a lime-water bath that had usually already been used for unhairing. The skins remained in this bath for about eight days (but twice as long in winter). In modern formulas the rinsed skins are not put into a lime-water bath, but placed over a wooden beam and trimmed on the flesh side with a blunt knife. This stretches them a little and removes dirt and remnants of flesh. It seems reasonable to assume that this was also done in the Middle Ages.
In the Middle Ages unhairing was done on the wooden beam straight after the lime-water bath. Modern formulas sometimes refer to a 'lime dressing' applied to the grain side of the skins, after which unhairing takes place. However, lime water was also used.
In the course of the nineteenth century, sodium sulphide was added to the lime water to speed up the unhairing process. During unhairing - with a curved or straight knife - the hair roots and the content of the sebaceous and sweat glands were also removed as much as possible. The skins were then put into a fresh lime-water bath (about eight days in the Middle Ages, one to three weeks in around 1900, depending on the size of the skins). This opens the skins up for the new, fresh lime and care must be taken not to 'burn' the skins with an excessively strong lime solution. After removal from the lime water the skins are returned to the wooden beam to be scraped clean once again on the flesh side.
Threads attached to tapered wooden pegs are then fastened to the edge of the wet skin. The pegs in turn are inserted in holes around the edge of a square, round or rectangular stretching frame. By turning the pegs the skin can be stretched into a smooth, creaseless surface. Stretch drying is essential for making parchment for it causes the fibres to lie in a flat plane parallel to the surface. Stretching also makes the parchment opaque. Rewetting manufactured parchment allows the stretched fibres to relax with the result that when the material dries again it becomes rough and horn-like. Consequently, parchment should only be dampened if it is allowed to dry in a stretched condition.
In the medieval formula stretched skins are scraped on the flesh side with a sharp, semicircular knife (drawing 7), and left to dry in the shade for two days. After drying they are dampened again and the flesh side scraped with powde-red pumice.
In modern formula preparations the skin is also scraped smooth on the flesh side with a similar semicircular knife. Scraping is accompanied by the continuous addition of lime water. For this operation slaked lime is used, prepared by temporary exposure to air in order to diminish the etching effect. During this treatment the stretcher is in a horizontal position, with the flesh side up. The grain side is treated only with powdered chalk, which has a polishing effect. This is followed by further polishing with pumice or powdered pumice. Split skins are treated in the same way on both sides. Scraping and polishing is done several times until all loose fragments of skin on the flesh side and the papillary layer of the grain side have been removed. Removing the papillary layer is important because it also removes the pigmentation from the skin (black-patched calves!).
After scraping and polishing the parchment is dried in the shade for some days. When it is thoroughly dry, it is taken from the stretcher and, if necessary, cut to measure.
The old and the later formula preparations use much the same method of treatment. Similarly, tools and equipment, such as stretchers and knives, are virtually the same. In eight hundred years little has changed in the manufacturing of parchment; the main difference between then and now is in the use of chemicals. Modern machines make it possible to split the skins to the required thickness before they are turned into parchment. This produces a flesh split and a grain split. In antiquity sheepskins were also split into two layers, without the help of machines. This was possible because sheepskins consist naturally of two clear layers separated by a loose, fatty layer. The practice of splitting skins ended after the 3rd century, however. In order to give both sides of the skin the same surface, the grain was scraped off with a razor-sharp, semicircular or round knife. A knife-sharpener was used to make a burr on the edge of the blade, thus turning it into a kind of scraper. With the grain removed, the surface became velvety to the touch. This parchment was particularly suitable for books, because there was little difference between the verso and recto sides of the pages.
Nowadays, too, the grain is often scraped (using machines and sandpaper) instead of being split. Where the whole skin (grain and fibre network layer) is left unscraped, as for instance for bookbinding parchment, pigmentation is removed with alum, enzymes or a bleaching agent (hydrogen peroxide).Like leather, parchment is also given various trivial names. Many of the terms we use hail from abroad, and this may cause confusion. It all started in France, where the term velin was used alongside parchemin. This gave rise to vellum which is used especially in Great Britain and, sometimes incorrectly, in the Netherlands. The British parchment manufacturer makes a distinction between parchment and vellum. Parchment is traditionally used for the split skin, vellum for the complete skin. In British technical jargon the terms sheepskin vellum and sheepskin parchment are used, although not always consistently. Dutch terms such as francijn and forril give no indication as to either the original animal or the method of manufacture.
It is important, especially for documentation relating to parchment conservation, that the terminology used be as unambiguous as possible. For parchment, as for leather, this publication has adopted the terminology as used in Kneep en Binding where parchment is defined as an 'animal skin, preserved by treatment with lime, stripped of hair and remnants of flesh, and dried while stretched, which causes the arrange-ment of the skin fibres to change, and its characteristic qualities to appear (slight thickness, a certain transparency and a light colour). It is sometimes possible to distinguish between the hair side (traces of hair pores; often smoother) and the flesh side (rougher structure); but some forms of treatment make it almost impossible to make this distinction.
Most parchment is made from sheep, goat or calves: sheep, goat or calf parchment; these are distinguished mainly by the hair patterns.'