earthenware vs slipware

earthenware

noun
  • An opaque, semi-porous ceramic made from clay and other compounds. 

slipware

noun
  • A type of pottery identified by its primary decorating process where slip is placed onto the dry surface by dipping, painting or splashing. 

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