black as Newgate's knocker vs swart

black as Newgate's knocker

adj
  • Completely black in colour. 

swart

adj
  • Black. 

  • Of a dark hue; moderately black; swarthy; tawny. 

noun
  • Black or dark dyestuff. 

verb
  • To make swart or tawny; blacken; tan. 

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