black as Newgate's knocker vs black as a dog's guts

black as Newgate's knocker

adj

  • Completely black in colour. 

black as a dog's guts

adj

  • Utterly black; pitch-black. 

How often have the words black as Newgate's knocker and black as a dog's guts occurred in a corpus of books? (source: Google Ngram Viewer )