The problem of the black finger has always been a mystery. Even though a ring can be 14K gold or higher alloy, a person’s finger can suddenly turn black. Usually this can last from a day to many weeks but the problem usually goes away. Unless the ring was created with a high percentage of nickel alloy, the ring itself is not the problem. I will list many possibilities and solutions.
Metallic abrasion. (Gold smudge.) The most common reason why skin discolors when wearing gold jewelry is metallic abrasion. The blackness is caused by the ring rubbing on makeup left on the hands. On the Moh’s scale of hardness, gold is about a 3. Many makeup powders contain compounds like calamine. These powders are actually small particles of rock which abrade small specks of gold which attach to the skin resulting in a dark appearance. Finely divided metal is not shiny but appears as black dust. When this dust comes into contact with skin, it sticks creating a black smudge. One can consider switching cosmetics or to wash hands thoroughly with soap and water after applying makeup before putting on jewelry.
The following situations can interact with or change a person’s body chemistry:
High acid food and drink. Eating foods or drinks that are high in acid like; tomatoes, pickles, coffee, wine, fruit juices, oranges, etc.
Iron deficiency. Take your gold ring and draw an invisible line down the inside of your arm. If the ring leaves a grayish black trail (called black dermographism) that may mean one has an iron deficiency.
High sodium. If one has eaten a higher-than-normal amount of salt, like salted popcorn, potato chips, etc.
Prescription drugs. Certain medications like anti-depressants, some antibiotics or even multivitamins.
Cleaning products and chemicals. Direct contact with bleach, ammonia, chlorine, etc., can cause a chemical reaction to gold jewelry.
Menopause. Woman in menopause can experience body chemistry and hormonal changes that make oxidation more possible while their body is adjusting.