The crucial difference between medieval and ancient methods of parchment processing lied in the fact that in Middle Ages slaked lime was used to unhaired hides. This method was probably brought by Arabs about the eighth century. The procedure of parchment making was following. First washed skins were limed by placing them for (in summer) to six weeks(in winter) in milk of slaked lime(5-10 % calcium hydroxide CA(OH)2), or by covering them for two or three weeks with 30% slaked lime paste. The use of the calcium lye was to intended to solubilize the epidermis and saponify the fat. The solubilization of epidermis cause the hair was easy to remove from the hair follicles. The nest stage consisted in washing the skins with running water, in order to remove the remaining lime liquor following that hair and remainder of the epidermis were scraped of together with some sticking out bits of flesh and the subcutaneous tissue. Thus purified skins were placed in pits filled with lime water and left to stand for three weeks; after being soaked for three or four days , skin was taken out to rest, only to be drenched again in lime water for three or four days. Such a procedure caused to skin to swell and soften. Then the skins were tightened on rectangular or circular frame on which they were to dry under tension. This constituted the key of parchment processing. The result of the above mentioned process was the typical flatted arrangement of collagen fibres. The viscous fluid present among fibres of the wet skin and containing a certain amount of the ground substance, dried in the form of hard, glue like substance, and fix the fibres in a stretched condition. Once stretched during the drying under tension, the fibres could not be restored to their original, relaxed state. During the drying the air-filled regions present in the stress-dried skin hinder the fibres from gluing and thus make the skin relatively elastic.
Both side skin were scraped with sharp, crescent shaped knife . This is a moon knife. (the latin name, lunellum or lunellarium is much more difficult to remember…) They are used to trim leather and hides. I use them to scrape the skins and remove extra gunk and water from the skin. If the blade is sharp enough, you can use it to shave the skin after it is dry, a very delicate operation. In the end parchment was smoothed out with pumice stone, the reaming greases was remove by rubbing chalk caused alkaline reaction of parchment, which made it less sensitive to acid air pollution.
If parchment was intended for use as writing materials, it required various finishing operations, in which medieval parchment excelled. Most valuable manuscript were partly or total dyes e.g. purple (with snail Purpurin)
Historically, Tyrian purple was extracted from sellfisch of the Murex genus such as Hexaplex trunculus and Murex brandaris. The name comes from the habitat of the molluskus , traditionally harvested near Tyre in the eastern Mediterranean.
Purples are caught with a sort of small wicker basket cast into the deep, and containing as bait bivalves which snap their shells together, as mussels are known to do. These bivalves, though half-dead, revive on returning to the sea and gape open greedily. The purples seek them out and attack them with protruding tongue, but the mussels shut up as soon as they feel the sting, and hold their assailants fast. Thus suspended, the purples are taken up, caught by their own greed. Another finished operation were employed in Greece. The surface was spread with egg and linseed oil and become glazy. This undercoat was necessary because otherwise thick paint layers in Greek miniatures could be flaked off.
Parchment is extremely susceptible to humidity even more than paper and hydroscopic. The fluctuation of the air relative humidity level in store room may bring about consideration change in the amount of water contained by parchment. An increasing level humidity from 10 % to 95% caused water content in parchment increase by about 30 % in relation to its mass. The time of water absorption is shorter than the time that is needed to dry. Humidity permeating the fibres caused collagen hydration; consequently parchment sheets swell and gain a certain degree of elasticity. Then parchment is dried from this relaxed condition, its properties are lost, and a hard transparent and horny sheet with various degree of surface waviness is obtained. This process called gelatinization is reversible, but substantial conservation work is needed to remedy harmful effects.
By this time its no secret that as long as parchments are stored under reasonable condition, they are remarkably durable and may persist over many centuries.
Enjoy Your Sunday !!!!!!!!!!!