filigree vs openwork

filigree

noun
  • A delicate and intricate ornamentation made from platinum, gold or silver (or sometimes other metal) twisted wire. 

  • A design resembling such intricate ornamentation. 

verb
  • To decorate something with intricate ornamentation made from gold or silver twisted wire. 

openwork

noun
  • Any of several forms of metalwork or needlework having decorative openings. 

  • A quarry; an open cut. 

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