dross vs sluice box

dross

noun
  • A waste product from working with metal. 

  • Worthless or trivial matter. 

  • The impurities in metal. 

  • Waste or impure matter. 

  • Residue that forms on the surface of molten metal from oxidation. 

verb
  • To remove dross from. 

sluice box

noun
  • A box with riffles along the bottom, used to trap heavier gold particles as water washes them and the other material along the box. 

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