kaoline vs paper clay

kaoline

paper clay

noun
  • Clay mixed with shredded paper or other fibres, valued for its strength and light weight in the production of large ceramic works. 

  • A kind of uniformly light-coloured clay composed of fine particles, used in the production of paper and wallpaper; kaolin. 

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