cave painting vs graffito

cave painting

noun
  • The paintings resulting from this activity regarded collectively, especially if prehistoric; cave art; (countable) an individual painting of this type. 

  • The activity of applying pigments to the interior surfaces of caves to create images, especially when carried out in prehistoric times. 

graffito

noun
  • A single instance of graffiti in the art/vandalism sense. 

  • An informal inscription, as by a worker or vandal. 

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