With the crux as the symbol of He who is believed to be the Light of the world, it may not matter that "crucible," derived from a lamp, has roots other than Latin. To the just-plain-folks of the day (as ignorant as I of the etymology of "crucible,") a "little cross" providing light seems to me a straightforward link.

"I don't know which is worse: ignorance or apathy. And, frankly, I don't care." - Anonymous