gesso vs gypsum

gesso

noun
  • A mixture of plaster of Paris and glue used to prepare a surface for painting. 

  • A work of art done in gesso. 

gypsum

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

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