Silver-plated items, whether decorative or functional, are popular for their brilliant luster and appearance of luxury. The answer is definitively yes: silver plate does tarnish, a natural chemical process that affects all items with a silver surface. This discoloration is the visible result of a reaction between the silver and compounds found in the air. Understanding the composition of silver plate and the specific chemistry of this reaction helps in both effective cleaning and long-term preservation.
The Composition and Nature of Silver Plating
Silver plating deposits a thin layer of pure silver onto a base metal core, such as copper, brass, or nickel. This technique involves electroplating, where a substrate is submerged in a solution containing silver ions. An electric current is then applied, causing the silver to bond to the surface of the base metal. The resulting layer of silver is typically very thin, often measured in micrometers, and is usually high-purity silver. This thinness is the main difference between silver plate and solid sterling silver (92.5% silver alloy). While both surfaces tarnish at the same rate, the thin plated layer is vulnerable to wear; aggressive treatment can quickly erode the coating and expose the underlying base metal, known as “wearing through.”
The Chemistry Behind Silver Plate Tarnish
Tarnishing is a chemical change, not a simple accumulation of dirt or grime, occurring when silver atoms react with sulfur compounds present in the atmosphere. The primary culprit is hydrogen sulfide gas (\(\text{H}_2\text{S}\)), which exists naturally in the air, often originating from sources like industrial pollution. When silver (\(\text{Ag}\)) contacts hydrogen sulfide, a chemical reaction forms silver sulfide (\(\text{Ag}_2\text{S}\)), creating a thin, opaque layer that appears black or dark brown. The reaction is accelerated significantly by environmental factors such as high humidity and elevated temperatures. Sulfur compounds found in items like eggs, rubber bands, wool felt, and latex-based paints can also hasten the tarnishing process upon direct contact.
Cleaning and Restoration Methods
The delicate nature of silver plate requires that tarnish removal methods are gentle to avoid wearing away the thin coating.
Traditional Polishing
Traditional commercial silver polishes are effective when applied with a soft cloth, such as a microfiber or cotton flannel, using light pressure. The polish contains mild abrasives and chemical agents that physically lift the silver sulfide layer from the surface. Because the silver layer is so thin, it is important to polish only until the tarnish is gone, minimizing the amount of silver removed during the process.
Electrochemical Cleaning
A highly effective and non-abrasive method is electrochemical cleaning, which reverses the tarnishing reaction. This technique involves placing the tarnished item into a bath of hot water, baking soda, and salt, with a piece of aluminum foil lining the container. The aluminum acts as an electrode, creating a reaction where the sulfur atoms transfer from the silver sulfide (\(\text{Ag}_2\text{S}\)) back to the aluminum, chemically reducing the silver sulfide back into pure silver and leaving the tarnish on the foil.
After either method, the piece should be rinsed thoroughly with clean water and dried immediately with a soft cloth to prevent water spots. Avoid chemical dips, which can be too aggressive, and never use abrasive materials like scouring pads or harsh household cleaners, as these will scratch the surface and quickly expose the underlying metal.
Preventing Future Tarnish
Since the reaction that causes tarnish is constantly occurring in the atmosphere, preventative care is the most effective way to maintain the luster of silver-plated items. Storing silver in a low-humidity environment is a primary defense, as moisture significantly accelerates the chemical reaction; items should also be kept away from heat sources and direct sunlight. Proper storage involves minimizing the silver’s exposure to atmospheric sulfur by placing pieces in specialized anti-tarnish bags or chests lined with treated flannel cloth. Alternatively, wrapping individual pieces in acid-free tissue paper or unbleached cotton muslin before sealing them in airtight polyethylene bags creates an effective barrier. It is advisable to keep silver away from high-sulfur materials (like rubber bands or felt), and using anti-tarnish strips or white chalk inside storage containers helps absorb residual moisture and sulfur.