The process of refining metals is referred to by way of illustrations in Isa 1:25; Jer 6:29; Zec 13:9; Mal 3:2-3.

He who reduced the metal to fluid by heat and solvents, as borax, alkali or lead (Isa 1:25; Jer 6:29), to remove the dross. His instruments were the crucible or furnace ("fining pot," Pr 17:3) and the blowpipe or bellows. Affliction removes the dross from the godly (1Pe 1:7). But the fiery ordeal only hardens the reprobate (Jer 5:3; Isa 9:10). Translated for "tower" and "fortress" (Jer 6:27), "I have set thee for an assayer and explorer," separating the metal from the dross "among My people." In Mal 3:2-3, Christ "shall sit as a refiner and purifier of silver, and shall purify the sons of Levi." The purifier sits before the crucible, fixing his eye on the metal, taking care the heat is not too great, and keeping the metal in only until, by seeing his own image reflected in the glowing mass, he knows the dross is completely removed. So the Lord with His elect (Ro 8:29; Job 23:10; Ps 66:10; Pr 17:3; Isa 48:10; Heb 12:10).

God is the refiner of His people, as the precious metals have to be separated from the dross that clings to them. Pr 25:4 (where the A.V. has 'finer'); Isa 48:10; Zec 13:9; Mal 3:2-3. So God tests the believer's heart (1Th 2:4), and his faith, which leads to endurance. Jas 1:12; 1Pe 1:7.

Refiner,

The refiner's art was essential to the working of the precious metals. It consisted in the separation of the dress from the pure ore, which was effected by reducing the metal to a fluid state by the application of heat, and by the aid of solvents, such as alkali,

Isa 1:25

or lead, Jere 6:29 which, amalgamating with the dress, permitted the extraction of the unadulterated metal. The instruments required by the refiner were a crucible of furnace and a bellows or blow-pipe. The workman sat at his work,

Mal 3:3

he was thus better enabled to watch the process, and let the metal run off at the proper moment.