branding iron vs ironstone

branding iron

noun
  • A piece of metal bent into a distinctive shape, heated and used to brand livestock. 

ironstone

noun
  • A type of vitreous pottery similar to stoneware 

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

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