ironstone vs steam iron

ironstone

noun
  • Any ore of iron which is impure through the admixture of silica or clay. 

  • A type of vitreous pottery similar to stoneware 

steam iron

noun
  • A smoothing iron that includes a system for spraying steam onto the item being ironed. 

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