black coal vs ember

black coal

noun
  • coal 

  • high-quality coal 

ember

noun
  • A glowing piece of coal or wood; a hot coal. 

  • Smoldering ash. 

adj
  • Making a circuit of the year or the seasons; recurring in each quarter of the year, as certain religious days set apart for fasting and prayer. 

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