clayware vs porcelain

clayware

noun
  • Articles made from clay. 

porcelain

noun
  • An object made of porcelain, (particularly) art objects or items of tableware. 

  • Synonym of cowrie. 

  • Synonym of china: porcelain tableware. 

  • A kind of pigeon with deep brown and off-white feathers. 

  • A hard white translucent ceramic, originally made by firing kaolin, quartz, and feldspar at high temperatures but now also inclusive of similar artificial materials; also often (figurative) such a material as a symbol of the fragility, elegance, etc. traditionally associated with porcelain goods. 

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