Crucible descends from Medieval Latin crucibulum, a word whose earliest recorded sense was "night lamp" before it came to mean a metal-melting pot, and its resemblance to Latin crux, "cross," is coincidental rather than a real etymological link, however much that resemblance later shaped the word's figurative meaning. The crucible appears constantly across medieval and early modern alchemical and metallurgical illustration, the plain workhorse vessel standing in nearly every scene that shows a furnace, used wherever a substance needed heat too intense for glass or unfired clay to survive. That constant association with severe heat gave the word its lasting figurative sense in English, a "crucible" as a severe trial or test, first recorded in the 1640s and still current today, entirely separate from the physical object.
The object itself needed almost no reinvention to cross from alchemy into chemistry and industry: a crucible, now most often made of graphite, porcelain, or specialized ceramic rather than plain fired clay, remains standard equipment today in chemistry laboratories, metal foundries, and jewelry workshops, doing precisely the job it has always done under precisely the name it has always carried.