Gold
Almost nothing attacks it, which is why the damage that does happen is nearly always done by the person cleaning it.
In detail
Gold is the most chemically stable metal a household is likely to own, and that fact does the opposite of what people expect: it means a dull gold ring is dirty rather than tarnished, and a mild detergent and a soft brush handle almost everything. Reaching for a metal polish instead is where the harm starts. What is worn is rarely pure. Jewellery gold is an ALLOY — the other metals give it hardness and colour — and those metals are not stable the way gold is, so a piece can discolour where gold would not. That is a fact about the copper or silver in it. The governing warning from conservation is that cleaning and polishing REMOVE ORIGINAL METAL, and that metal cleaners may leave residues that generate further corrosion. On solid gold that loss is slow and survivable; on anything plated it is not. Storage does more than cleaning. Sulphur is the strongest tarnishing agent and is given off by wool, felt, foam rubber and paint as well as by urban air — so the lined box a piece lives in may be the reason it looks dull. And where a piece is set with stones or its composition is uncertain, a specialist is the right answer rather than a guess at the chemistry.
Why
- Gold is explained by Polishing removes metal
Sources for this page
Sources
Museum Handbook Part I, Appendix O: Curatorial Care of Metal Objects
National Park Service, US Department of the Interior, 2002 · Reference work
Relied on for: That an alloy is made by combining metals to modify their properties, that cleaning and polishing remove original metal, that over-cleaning loses information from the object, that metal cleaners may leave residues generating further corrosion, and that sulfur compounds are the strongest tarnishing agents and are generated by wool, felt, foam rubber and paints. (states this directly)