black coal vs cinder

black coal

noun
  • coal 

  • high-quality coal 

cinder

noun
  • Partially or mostly burnt material that results from incomplete combustion of coal or wood etc. 

  • An ember. 

  • Slag from a metal furnace. 

verb
  • To cover with cinders. 

  • To reduce to cinders. 

How often have the words black coal and cinder occurred in a corpus of books? (source: Google Ngram Viewer )