#1: The probability that skin secretions and perspiration contain chlorides and sometimes sulfides. These chemicals combine with the molecules of silver and copper that are usually present in a gold alloy to form dark-hued salts such as silver chloride and copper sulfate. This reaction occurs usually in a woman only when pregnant.

#2: The possibility that outside chemical influences are to blame. A maritime or semi-tropical climate where chlorides from the sea can combine with normal skin secretions to form corrosive chemicals. Working in a plant where rubber tires are made, sulfides and skin secretions may tarnish a ring even if it is worn only awawy from work. Not to be overlooked is the possibility that a woman's cosmetics and/or detergent may contain chemicals that corrode her ring.

#3: Simple tarnishing. More and more areas in the world are becoming subject to industrial smog. Often these smog fumes are thick with sulfur dioxide from the burning of low-grade, sulfur-laden fules or contain other corrosive chemicals such as phosphates. These air pollutants can attack gold alloys directly, even when jewellery is not being worn. When a tarnished ring slips back on the finger, or a bracelet onto the arm, the thin film of tarnish rubs off in a black smudge.

#4: A possibility, but very rare, is a black dermographism, caused by tiny particles of dust or powder which become imbedded in the skin. In dry dusty geographical areas these partials float in the air, and when lodged in the skin, result in a sort of "human sandpaper" that can wear away specks of karat gold from a ring, bracelet or necklace.

#5 Least likely, an actual allergy to gold or other metals in the alloy. Nickel, found in most modern white gold alloys, is the worst offender. Some medical authorities have stated that nickel produces more instances of contact dermatitis than all the other metals put together. The other metals commonly found in karat gold alloys - gold, silver, copper and zinc - very rarely cause allergic dermatitis.