Sheepskin was used as an anti-fraud device in British legal documents for hundreds of years

(Sean Doherty, Jonathan Finch, University of York. Published: April 9, 2021 2.02pm BST)

The 16th and 17th centuries were a notably litigious period in British history. New rights, wealth and obligations had to be protected through legal transactions – and that needed documentation.

“A technique called peptide mass fingerprinting offers a new way to identify the species, by analysing proteins from the skin. Using this method, we examined 645 documents dated from 1499 to 1969, and found 96.4% of these were sheepskin.”

Delamination

Parchment is made from the dermis, a layer of skin which is divided into two parts. There’s the fine dermal fibres of the upper papillary dermis and the larger fibres of the lower reticular dermis. In sheepskin, the interface of these two layers is weak because of an abrupt change in structure and a large quantity of fat, which forms at the junction.

During the production of parchment, the skin is submerged in an alkaline solution which draws out this fat. In sheepskin, which has more fat than cow or goat skin, this process has the potential to leave voids between the two layers. If the surface of the parchment is scraped in an effort to remove or alter text, these two layers are likely to detach – known as “delamination” – leaving a large blemish on the surface.

This tendency of sheepskin to delaminate