Tarnish is the dull, darkened film that develops on metal surfaces due to a natural chemical reaction with elements in the environment. Unlike rust, tarnish is a thin, self-limiting layer of corrosion affecting only the outermost atoms of the metal. Since the precise composition of the discoloration depends on the metal, the cleaning approach must be carefully tailored to the material being treated.
Understanding Tarnish and Initial Assessment
Tarnish formation is driven primarily by exposure to sulfur compounds and moisture. Silver turns black or gray when it reacts with hydrogen sulfide in the atmosphere, creating silver sulfide on its surface (sulfidation). Brass and copper are more reactive, often forming metal oxides or carbonates, such as the green-blue layer called verdigris or a brownish film. High humidity and airborne pollutants accelerate these reactions, dulling the metal’s natural shine.
Before applying any cleaning agent, determine if the item is solid metal or merely plated. Plated items have only a microscopic layer of precious metal, making them susceptible to damage from abrasive cleaning methods. Prepare the surface by dusting away loose dirt and rinsing off any grime under warm water. When proceeding with restoration, wearing gloves and ensuring adequate ventilation is a standard safety measure.
Methods for Cleaning Silver
Silver is most often cleaned using non-abrasive methods to avoid scratching the relatively soft metal. The most effective technique for solid silver is the chemical reduction process, which reverses the sulfidation without removing any of the silver itself. This electrochemical reaction requires a heat-safe container lined with aluminum foil, hot water, and baking soda.
The silver item must be fully submerged and in direct contact with the aluminum foil within the solution. The aluminum acts as an anode, drawing the sulfur atoms from the silver sulfide tarnish to itself, effectively converting the black tarnish back into pure silver. Near-boiling water accelerates this transfer, which typically takes only a few minutes. After soaking, the silver must be carefully removed with tongs, rinsed thoroughly with clean water, and immediately dried with a soft cloth to prevent water spots.
An alternative approach for light tarnish or large items is using a paste application. A simple paste made from baking soda and water can be gently rubbed onto the surface with a soft, lint-free cloth. The mild alkalinity and fine crystalline structure of the baking soda provide a gentle polishing action to lift the discoloration. This paste method is safer for silver-plated items than the chemical reduction bath, which can compromise the thin plating layer. When cleaning plated pieces, apply minimal pressure to prevent wearing through the silver layer to the base metal underneath.
Restoring Brass and Copper Items
Cleaning brass and copper relies on using mild acids to dissolve the metal oxides and carbonates that form the tarnish layer. Natural acidic cleaners are highly effective for this purpose, eliminating the need for harsh commercial polishes. A common solution involves a paste of lemon juice and salt, where the citric acid in the juice reacts with the tarnish, and the salt acts as a fine, soft abrasive.
Another method uses a mixture of white vinegar and salt, applied directly to the surface with a soft cloth or sponge. For heavier discoloration, mix the vinegar and salt with flour to create a clingy paste, allowing the acid to work longer. After applying any acidic cleaner, the item must be rinsed immediately under warm water to neutralize the acid and then dried completely to avoid new spots.
Consider the history of the item, especially antique pieces, before starting a deep clean. The greenish-blue or deep brown surface layer on copper and brass, called a patina, is often desirable and adds character and value. Aggressively removing this patina by scrubbing or prolonged soaking eliminates the aged appearance. In such cases, perform only a light surface wipe to preserve its natural, aged aesthetic.
Preventing Future Tarnish
Once metal items are clean, proper long-term storage is the most effective defense against tarnish recurrence. Since the chemical reaction is triggered by airborne compounds and moisture, minimizing exposure to the atmosphere is the priority. Storing items in airtight containers, such as sealed plastic bags or specialty jewelry boxes, significantly slows the rate of tarnish formation.
For added protection, anti-tarnish strips or cloths can be placed alongside the metal to absorb sulfur-containing gases within the enclosed space. These materials chemically neutralize corrosive elements before they react with the metal surface. Controlling the environment also means avoiding areas with high humidity, such as basements or bathrooms, and using moisture absorbers like silica gel packets in storage areas. A gentle wiping of the metal with a soft cloth after handling removes skin oils and residues that accelerate the tarnishing process.