Wilhelm Rau (1974) comprehensively discussed metals in Vedic literature. (Rau, Metalle und Metallgeräte im vedischen Indien, 1974)
In this paper, focusing especially on the base metals “áyas-,” I investigate their usage in every stage of Vedic literature, referring widely to recent studies.
In the RV, áyas- is solely used as a general term for the base metals and there is no reference to its concrete name. In the stage of the Atharvaveda, áyas- is divided into two types, “black” (śyāmá-) and “red” (lóhita-), and other base metals like tin “trapú-” or lead “sī́sa-” become known. The situation in the YSm is almost the same, however, the word lohá-, the substantive for copper, is first used in a passage of the VS and TS.
A pair of passages in the black YSp (KS and MS) suggestively tells the property of pure copper; its high thermal conductivity. In the stage of ŚB, áyas- is no longer classified by color, and on the other hand, we can determine that it connotes specifically iron in some passages.
