The wearing of silver jewelry when manipulating photographic chemicals or solutions may cause staining of the skin. When silver is attacked by a chemical solution such as nitric acid, the solution of silver salt formed is reduced back to silver by the skin. This silver is in a finely divided form and causes an intensely black stain. Silver jewelry should be removed before working with photographic chemicals or solutions.
Medications in the wearer�s system, especially certain antibiotics, can also cause jewelry to blacken or discolor. In some rare cases, the wearer�s basic body chemistry reacts with the alloys in both gold and silver and causes tarnishing. Wearing a higher karat of jewelry may often have a solution to both of these situations: 18K or 22K instead of 14K.
This information is not offered as an excuse, but to clarify the reasons, provide the facts, and offer solutions for those who may encounter the problems described.
Other information, answers to your questions:
Fisher, Dr. Alexander A, What Causes Gold Smudges, Jewelers Circular-Keystone, March 1971.
Gardam, D.E., Why Jewelry Sometimes Blackens the Skin or the Clothing, The Worshipful Company of Goldsmiths, Special Report No. 4, October 1989.
Metallic Abrasion
Corrosion
The Tarnishing of Sterling Silver Jewelry
Is this Cheap Gold?
Saving your Jewelry from Chlorine
Fine Jewelry Care