Calfskin parchment (6)
I believe the answer is:
vellum
'calfskin parchment' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for vellum that I've seen before include "What was written on" , "Heavy cream-coloured writing paper" , "Heavy cream-coloured paper or parchment" , "Fine parchment made from calf-skin" , "Kind of fine parchment for writing" .)