Silver
Authority: Metalwork Care & Restoration Guides
Silver tarnishes when trace hydrogen sulfide in the air reacts with the surface to form black silver sulfide. Light tarnish lifts with a baking-soda paste or gentle calcium-carbonate polish; heavier tarnish needs commercial silver polish or fine steel wool. An aluminum-foil-and-baking-soda bath reverses tarnish electrochemically without abrading away any silver.
Routine Cleaning
Wash with warm water and mild dish soap using a soft cloth, then dry immediately and thoroughly, since silver spots easily if left to air dry.
Remove Light Tarnish
Rub gently with a paste of baking soda and water, or a small amount of calcium carbonate (whiting), using a soft cloth. These are mild enough to lift the silver sulfide layer without visibly scratching the surface, which is why museums use them on historic pieces.
Remove Heavy Tarnish
For heavier build-up, use a commercial silver polish, or very fine steel wool for stubborn spots. Work gently: unlike the baking-soda method, these techniques remove a microscopically thin layer of silver itself along with the tarnish.
Electrochemical Method (Aluminum Foil)
Line a bowl or pot with aluminum foil, add hot water with baking soda or salt, and submerge the silver so it contacts the foil. The reaction transfers sulfur from the tarnish onto the aluminum, converting silver sulfide back into metallic silver without abrading the surface.
Anti-Tarnish Storage
Store polished silver in tarnish-resistant cloth or a sealed anti-tarnish bag, away from rubber bands or rubber liners -- rubber is vulcanized with sulfur, the same element that reacts with silver to cause tarnish in the first place.
The Chemistry of Silver Tarnish
Silver tarnish isn't ordinary oxidation the way rust is. Silver is fairly unreactive with oxygen alone; what actually darkens it is trace hydrogen sulfide in the surrounding air, which reacts with the surface silver atoms to form silver sulfide, a black compound that builds up as the familiar dull, dark film. Because the reaction depends on airborne sulfur compounds rather than oxygen exposure, silver kept in a sealed, low-humidity environment away from sulfur sources tarnishes far more slowly than silver left out in open air.
This is also why some materials accelerate tarnishing on contact: rubber, for instance, is vulcanized using sulfur to cross-link its polymer chains, so silver stored touching rubber bands, rubber-lined drawers, or rubber gloves tarnishes noticeably faster at the point of contact.
Why the Foil Trick Works (and Abrasives Don't Quite)
Polishing compounds, steel wool, and commercial silver polish all remove tarnish the same basic way: they physically abrade the blackened surface layer away, taking a microscopically thin layer of the underlying silver with it. Done repeatedly over years, especially on pieces with fine engraved detail, this gradually softens the detail.
The aluminum foil method works differently. Submerging tarnished silver in hot water with baking soda or salt, in contact with aluminum foil, sets up an electrochemical reaction: aluminum is more reactive than silver, so it preferentially bonds with the sulfur, pulling it off the silver sulfide and depositing it onto the foil instead. The silver atoms are left behind on the piece rather than being scrubbed away, which is why this method doesn't wear down detail the way mechanical polishing does over time.