The making of parchment:

'Take an entirely new bath and place therein old lime (calcem non recentem) and water mixing well together to form a thick cloudy liquor. Place the skins into this, folding them on the flesh side. Move them with a pole two or three times each day, leaving them for eight days(and twice as long in winter).'

The lime penetrates the skin and at first attacks the soft parts. This is the fat and the albumen in and around the hair follicles, loosening the hair. The follicle is the spot in the skin where the hair grows. The lime also works into the albumen-rich parts which exist between the fibres of the skin. Soluble chalk deposits are formed. According to other recipes where old lime is mentioned it is more then likely that this refers to lime already used for removing hair. Unknown before the middle ages, and for a long time after, this forms natrium sulphide, a cemical that speeds up the process of unhairing and having a deeper penetration. The fleshside must be turned outward so that the lime can penetrate more easily. It is only possible to smeer the wet and swollen fleshside of the skin with lime. It is folded double with the fleshside on the inside and laid in a closed vat. The skins will then still remain damp enough for the hair to be removed without the hair getting into contact with the lime as happens with a lime bath. This is a particulary good method for removing clean wool from sheepskin. The recipe specifically mentions 'mixing well' because the lime must work evenly over the entire skin.