This refers to how gold and silver are refined. A metal is refined by heating it to a high temperature so that it melts and the impurities may be removed. Alternate translation: "The crucible is used to refine silver and the furnace is used to refine gold" (See: [[rc://en/ta/man/translate/figs-explicit]])
This speaks of Yahweh testing people to help them stop being evil and foolish as if their hearts were a metal that Yahweh was refining to remove everything that is impure. Alternate translation: "Yahweh tests peoples' hearts" (See: [[rc://en/ta/man/translate/figs-metaphor]])