sheathing vs vellum

sheathing

noun
  • Something that wraps around or surrounds something, as a sheath encases its blade. 

vellum

noun
  • A type of parchment paper made from the skin of a lamb, baby goat, or calf. 

  • A writing paper of very high quality. 

How often have the words sheathing and vellum occurred in a corpus of books? (source: Google Ngram Viewer )