bullion vs ingot

bullion

noun
  • A bulk quantity of precious metal, usually gold or silver, assessed by weight and typically cast as ingots. 

ingot

noun
  • A solid block of more or less pure metal, often but not necessarily bricklike in shape and trapezoidal in cross-section, the result of pouring out and cooling molten metal, often immediately after smelting from raw ore or alloying from constituents. 

verb
  • To form (scraps of metal) into ingots. 

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