During most of the Middle Ages the books were created with skins of animals, commonly known as parchment, used instead of vegetal fibers which replaced it almost entirely since the 14th century.
Below: illustration representing the preparation of parchment
Parchment was prepared in different ways depending to the method utilised. Generally the skin was first of all cleaned in order to remove blood and dirt, then submerged in a strong alkaline solution (water and chalk) for then proceeding to the removal of hair residue. After this it was taken away all the pieces of flesh still stuck in the parchment, and then going towards the drying phase while taut, similarly to the skin of a drum, for approximately one week time. Once the skin was dry it was then ready to be cut and used for writing purposes.
During the most delicate working phases when the artisan was using the quarte moon knife to remove the hair and flesh residues, it could happen that the parchment would get ruined through the production of small holes. In that case the paper was not thrown away but still sold, even though at a lower price than the perfect one. Different sources report how the parchment was sold in 4 different prices, depending to the quality of the manufacturing and the presence or not of imperfections such as holes or creases. The information about the imperfections is today extremely important not only from a graphics point of view but also because it indicates to the historians how precious a manuscript was considered during the phases of the making. The Codex Gigas for example, also known as the Devil’s Bible, is completely flawless when it comes to its parchment.
The holes were mended by sewing with silk its irregularities or by inserting the holes inside some graphic content.
Above: book from the 14th century from the monastery of Vadstena, Sweden. The mending was realised with silk in different colours
Sometimes, depending to the attitude of the amanuenses towards the parchment, the holes were not fixed but instead they were becoming part of the graphics of the book.
Below: book from the 9th century of the Berlin State Library, the dragon was drawn behind the hole, left in its original form
Below: the hole becomes the face of a man with bear and moustache
Below: sometimes the tears were so important to force some sort of restoration, like in this example
Below: even the pages partially ripped were sewed back up in order to optimise the costs
Below: the parchment underneath did not only present a hole but it had also an irregular edge, details which drop its value quite a bit, most likely