nacreous vs polychromate

nacreous

adj
  • Exhibiting lustrous or rainbow-like colors. 

  • Of, or resembling nacre (mother of pearl). 

polychromate

adj
  • Composed of many colours 

noun
  • A salt or ion composed of multiple chromate groups 

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