lambskin vs parchment

lambskin

noun
  • The skin of a very young sheep, especially prepared with the fleece still attached. A very fine form of leather. 

  • A kind of woollen cloth resembling this. 

parchment

noun
  • Material, made from the polished skin of a calf, sheep, goat or other animal, used like paper for writing. 

  • A document made on such material. 

  • The creamy to tanned color of parchment. 

  • The envelope of the coffee grains, inside the pulp. 

  • Stiff paper imitating that material. 

  • A diploma (traditionally written on parchment). 

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