crystal vs watch glass

crystal

noun
  • The glass over the dial of a watch case. 

  • A fine type of glassware, or the material used to make it. 

  • Crystal meth: methamphetamine hydrochloride. 

  • A solid composed of an array of atoms or molecules possessing long-range order and arranged in a pattern which is periodic in three dimensions. 

  • A piece of glimmering, shining mineral resembling ice or glass. 

adj
  • Very clear. 

  • "Do I make myself clear?" / "Crystal." 

watch glass

noun
  • The glass covering of the face of a watch. 

  • A sandglass. 

  • An item of glass laboratory equipment consisting of a simple, slightly concave circle of glass. It is a general utility item, used to hold small samples, to evaporate liquids, to cover a beaker, and so on. 

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