The making of parchment:

I shall begin with a general overview of the process of parchment making. For this purpose using a recipe from the twelfth century. This can be considered as essentally the basic process, one that I and others in other lands still use. Variations on this will be described later.

To begin with we must know the material used in the preparation: slaked lime (calcium carbonate). Indeed the definition of parchment is: a skin treated with slaked lime which is dried in a stretched way.

This cooled slaked lime retains the ability to work into materials for some time. An animal skin immersed for a month in slaked lime will be considerably digested. This characteristic of lime was first discovered as far back as the third century ans its use is unchanged from the middle ages to the present time.

How parchment was prepared before mediaeval times is uncertain. It is thought that salt and flour made acid in water was used but there is also the probability that chicken or dog excrement was used, and who knows what else!

The basic technique
The already mentioned early twelfth century recipe is one of the more detailed examples and it as follows.

Take goatskins ( 1 ) and stand them in water for a day and a night. Take them and wash them till the water runs clear ( 2 ). Take an entirely new bath and place therein old lime (calcem non recentem) and water mixing well together to for 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) ( 3 ).
Next you must withdraw the skins and unhair them ( 4 ). Pour off the contents of the bath and repeat the process using the same quantities, placing the skins in the lime liquor, and moving them once each day over eight days as before ( 5 ).
Then take them out and wash them well until the water runs quite clean ( 6 ). Place them in another bath with clean water and leave them for two days ( 7 ).
Then take them out, attach the cords and tie them to the circular frame ( 8 ). Dry, then shave them with a sharp knife, after which, leave for two days out of the sun…( 9 ) moisten with water and rub the flesh side with powdered pumice ( 10 ). After two days wet it again by sprinkling with a little water and fully clean the flesh side with pumice so as to make it quite wet again ( 11 ). Then tighten up the cords, equalise the tension so that the sheet will become permanent. Once the sheets are dry, nothing further remains to be done ( 12 ).

Schedula diversarium artium
Theophilus Presbyter. Early twelfth century
Britisch Museum MS. Harley 3915, fol. 128r

So much then concerning the basic process, in the following article the history of parchment making will be discussed. Meanwhile here is the manufacture process in diagram form.