#13 Sammakko—Sind 'crucible' und 'melting pot' exakt gleichbedeutend?
In the one original sense of the word, yes:
1. a. A vessel, usually of earthenware, made to endure great heat, used for fusing metals, etc.; a melting-pot."
---and at the start of the notes on etymology: "medieval Latin crucibulum, -bolum, originally a night-lamp, later a melting pot for metals" (!)
---on the relation to L. crux, etc.: "Apparently a derivative of Latin crux, crucis Cross ... and see Du Cange, Littré, Hatzfeld, who suggest for the original sense ‘lamp with crossed wicks giving 4 flames’, but this is doubtful ... "
---curiously enough, though, in OED under "melting pot" there is a sense (not the first listed, of course) that goes a little in the direction of the second metaphorical sense of "crucible" (i.e., at #2 above):
3. fig. a. A situation in which things are constantly changing and the outcome is uncertain."