Tin is one of the earliest metals known and used. Because of its hardening effect on copper, tin was used in bronze implements as early as 3,500 B.C., although the pure metal was not used until about 600 B.C.

Chromium (Cr) is a hard, bluish metallic element. The only ore of chromium is the mineral chromite and 99 percent of the world’s chromite is found in southern Africa and Zimbabwe. Geologists estimate that there are about 11 billion tons of mineable chromite ore in the world, enough to supply the current demand for hundreds of years.

Lead (element #82, symbol Pb) is a very soft, blue-gray, metallic element. It is primarily produced from the mineral galena. It has been used since antiquity.