crucible vs melter

crucible

noun
  • The bottom and hottest part of a blast furnace; the hearth. 

  • A heat-resistant container in which metals are melted, usually at temperatures above 500°C, commonly made of graphite with clay as a binder. 

  • A cup-shaped piece of laboratory equipment used to contain chemical compounds when heating them to very high temperatures. 

  • A very difficult and trying experience, that acts as a refining or hardening process. 

melter

noun
  • A furnace used for melting iron in a foundry. 

  • A laborer who operates such a furnace. 

  • A person or thing that melts. 

  • A variety of peach in which the flesh parts freely from the stone when ripe, also known as a free-stone. 

  • An obsolete spelling of milter. 

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