Paul Stroble, in Advent 2009, Celebrate the Newborn Jesus, explains these terms:
Malachi uses two different images of refinement. The first is the image of fire that purifies gold and silver. Gold and silver are precious for their rarity, beauty, and malleability. Gold is durable and does not oxidize. When gold is heated, it melts and becomes better as the impurities are burned off. .... The second is the image of the preparation of newly woven cloth. A fuller was a person who prepared new cloth, and fullers' soap was a strong alkali that cleansed the cloth.Stroble then asks, "What times in your life were refining?"