ironstone vs smoothing iron

ironstone

noun
  • A type of vitreous pottery similar to stoneware 

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

smoothing iron

noun
  • A heated appliance that is used to smooth clothing and other items after washing and (usually, partially) drying. 

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