Silver Corrosion
Silver (Chemical symbol Ag) is a brilliant gray white metal that is quite soft and malleable. It is quite resistant to corrosion and does not oxidize easily, although it readily forms a surface tarnish of silver sulfide.

Of all the metals, it is the best conductor of electricity. Due to these qualities (and its relative scarcity), it is often classified along with gold and platinum as a precious metal. Silver's primary use is in photographic paper and film 28% (commercial photography, medical, dental and industrial X-rays and graphic arts), jewellery and electronics 25% (connectors, contacts and batteries).
The main source of silver is in lead ore, although it can also be found associated with copper, zinc and gold and produced as a by-product of base metal mining activities. Mexico, Peru and the USA are major producers of silver. There are many substitutes for silver in a variety of applications. Most importantly is the advance of digital imaging that no longer requires image development using silver related products. The use of stainless steel for ornamental tableware is replacing traditional silver. Aluminum and rhodium can be used instead of silver in mirrors and other reflective applications.

Gold Corrosion

Gold is the most non-reactive of all metals and is benign in all natural and industrial environments. Gold never reacts with oxygen (one of the most active elements), which means it will not rust or tarnish. Gold tarnish is very thin and shows up as a darkening of reflecting surfaces.

Gold is among the most electrically conductive of all metals. Since electricity is basically the flow of charged particles in a current, metals that are conductive allow this current to flow unimpeded. Gold is able to convey even a tiny electrical current in temperatures varying from -55° to +200° centigrade.

"Purple plague" is a brittle gold aluminum compound formed when bonding gold to aluminum. The growth of such a compound can cause failure in microelectronic interconnection bonds.

Gold Tarnishing
Possible causes include:

• Perspiration (everyone's body chemistry is different, hence this is why some are more susceptible than others); for women, the time of the month can influence their body chemistry.
• Perfume, hair or deodorant sprays,
• Tarnishing during storage (storage boxes may contain organic sulfur compounds),
• Leaching of acid/ cleaning solutions from surface microporosity from cast jewelry; this causes corrosion locally (such porosity may even trap perspiration during wear, causing local corrosion)
• Preparation of vegetables such as onions and spices (many foodstuffs contain sulfur compounds and others are also acidic).

Another possible mechanism may be surface micro-porosity on the surface of investment (lost wax) cast items. This porosity may trap acids and other cleaning solutions, sprays, or perspiration and cause a local corrosion which 'creeps' over the surface of the item.

The tarnish films formed are generally harmless although unsightly and may lead to a black smudging of the skin. Such films can be easily polished off by a jeweler to restore the bright gold color.