The impurities of silver separated from the one in the process of melting (Prov. 25:4; 26:23; Ps. 119:119). It is also used to denote the base metal itself, probably before it is smelted, in Isa. 1:22, 25.
Easton’s Bible Dictionary
Dross
Easton’s Bible Dictionary (1897), public domain. Text via Theographic Bible Metadata, CC BY-SA 4.0.