Blackening or discoloration of either the skin and clothing or the jewelry itself is certainly very annoying. There are several causes for these occurrences.
Cosmetics often contain chemical compounds which are harder than the jewelry itself.
Metallic abrasion occurs when these hard compounds come in contact with the jewelry metals and wear or rub off very tiny particles of metal which appear as jet black dust. Very finely divided metal always appears black rather than metallic. When this dust falls on absorbent surfaces, such as skin or clothing, it sticks forming a black smudge. To prevent this, cosmetics which contain zinc oxide, titanium dioxide, ferric oxide, and calamine should be avoided. If this is not possible, we recommend that you remove rings and other metal jewelry while applying cosmetics.