gypsum vs plaster cast

gypsum

noun
  • A mineral consisting of hydrated calcium sulphate. When calcinated, it forms plaster of Paris. 

plaster cast

noun
  • A cast made of a stiff material (often plaster of Paris and gauze) in order to immobilize a broken bone for the period of healing. 

  • A copy of a piece of art or other object cast in plaster. 

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