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Chemical composition of silver tarnish

I had taken as a given that silver tarnish is a layer of silver sulfide on the surface of a utensil, and that cleaning it using a thiourea based agent like Tarn-X dissolves the sulfide layer.

However, while recently cleaning a variety of tarnished sterling and silver plated utensils, I noticed (1) the sulfureous odors emitted during the cleaning process varied considerably from one piece to the next; and (2) the tarnish on a few pieces could not be removed completely via the non-abrasive chemical process.

Knowing that many foods such as members if the cabbage and onion families have various sulfur compounds in them as flavor and aroma components, and that the sulfur containing amino acids cysteine and methionine are almost universally present in living organisms (including those we eat), I wondered: is silver tarnish a complex mixture of silver complexes that might reveal a history of the foods a person has eaten. Sherlock Holmes would know for sure.

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