The sudden appearance of a dark film on a favorite piece of jewelry is often a confusing and frustrating experience. This blackening, commonly known as tarnish, is not a sign of poor quality, but rather a naturally occurring chemical reaction. The metals used in jewelry, particularly silver and copper, react with substances in the environment, creating a dark compound on the surface. Understanding the specific nature of this reaction and its common triggers is the first step toward preserving the luster of your treasured items.
The Chemical Reaction Behind Tarnishing
The primary cause of jewelry blackening is sulfidation, a type of surface corrosion. This reaction occurs when the metal, most commonly silver, interacts with trace amounts of sulfur-containing gases present in the air. The most notable of these gases is hydrogen sulfide, which is released from various natural and industrial sources.
When silver comes into contact with hydrogen sulfide and oxygen, it forms a new substance on the surface of the metal. This new compound is silver sulfide, which is dark brown to black and constitutes the tarnish layer.
While pure silver is the metal most recognized for tarnishing, the process also affects other metals commonly alloyed with it. Sterling silver, for instance, is 92.5% silver and 7.5% copper. The copper within this alloy can also react with sulfur, forming copper sulfide, which further contributes to the dark discoloration.
The rate of sulfidation is significantly influenced by the surrounding environment. High relative humidity and moisture act as catalysts, accelerating the chemical reaction between the metal and sulfur compounds. Jewelry stored in humid conditions will often tarnish more quickly than pieces kept in a cool, dry place.
Everyday Causes of Accelerated Blackening
While airborne sulfur triggers the initial reaction, certain factors in a person’s daily routine dramatically speed up the blackening process. Personal body chemistry plays a significant role, as sweat contains salts and acidic substances that accelerate the oxidation of jewelry metals. Natural oils and residues left on the metal surface after wearing trap moisture and corrosive agents, creating an environment where tarnish thrives.
External substances that come into direct contact with the jewelry are often the most aggressive culprits. Common cosmetic products like perfumes, hairsprays, lotions, and sunscreens contain chemicals that react with metal alloys. These products leave a sticky film that attracts and holds sulfur compounds and moisture close to the metal surface, rapidly darkening the jewelry.
Exposure to household cleaning products poses a serious threat to jewelry integrity. Cleaners containing bleach or ammonia are highly reactive and can cause rapid corrosion and pitting, particularly in gold alloys and sterling silver. Even certain foods, like onions or eggs, contain sulfur compounds that can be transferred to the metal, causing an immediate, localized reaction.
The presence of chlorine, such as in swimming pools or hot tubs, is particularly destructive to metal alloys. Chlorine does not just accelerate tarnish; it can attack and dissolve non-gold metals, like copper, leading to microscopic stress fractures and structural weakening. Furthermore, sulfur compounds released from materials like rubber bands and latex gloves can off-gas, causing discoloration even when the jewelry is not being worn.
Simple Steps to Prevent Jewelry Discoloration
Preventing discoloration involves minimizing the jewelry’s exposure to daily chemical accelerators. A practical strategy is the “last on, first off” rule: jewelry should be the last thing put on after applying cosmetics and the first thing removed at the end of the day. This simple habit limits contact with corrosive chemicals.
It is helpful to remove all jewelry before engaging in activities that involve moisture, chemicals, or excessive sweating. This includes showering, bathing, swimming in chlorinated water, and using household cleaning supplies. Since moisture accelerates the tarnishing reaction, any water contact should be followed by gently patting the piece completely dry with a soft cloth.
Proper storage is an important defense against airborne sulfur and humidity. Jewelry should be kept in a cool, dry place away from direct sunlight and never stored in a high-humidity area like a bathroom. Storing items in airtight containers or sealed plastic bags significantly limits their exposure to the open air.
Adding anti-tarnish strips or packets of silica gel helps to absorb moisture and residual sulfur compounds in the air. Finally, regularly wiping down pieces with a soft, lint-free cloth after each wear removes accumulated body oils, sweat, and residues. This maintenance step prevents a corrosive layer from building up on the metal surface before it has a chance to turn black.