crucible

noun

1. 1

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

2. 2

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

3. 3

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

4. 4

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