Plated jewellery does not fade evenly. Colour disappears from edges, ridges and clasp faces while recessed areas stay bright, and the pattern is set by how plating is deposited.
Plating is a microscopically thin layer
Electroplating deposits a layer of gold measured in microns onto a base metal. Standard costume plating is a fraction of a micron thick.
Heavier grades exist, described by terms indicating a minimum thickness and karat, and they last far longer for the straightforward reason that there is more metal present.
Nothing about the appearance of a new piece reveals which grade it is, because a very thin layer looks identical to a thick one when undamaged.
Current concentrates at high points
Electroplating is driven by an electric field, and that field is not uniform across a shaped object. It concentrates at points and edges and weakens in recesses.
Counterintuitively, this deposits more metal on protruding areas and less in hollows, which is why manufacturers rotate and rack pieces carefully.
Complex shapes with deep recesses plate unevenly regardless, so a piece can carry a nominal thickness that is not achieved everywhere on its surface.
Wear concentrates in the same places
Edges, ridges and clasp surfaces are where a piece contacts skin, clothing and other jewellery, so they receive nearly all the abrasion.
Even a well-plated high point is thin relative to the friction it receives, and mechanical wear removes metal much faster than any chemical process.
Recessed areas are protected by geometry, which is why an old chain often retains colour deep between links while the outer faces have gone.
The base metal decides what happens next
Over brass or copper alloys, exposed base metal oxidises and can leave green marks where sweat carries dissolved copper onto skin.
Over sterling silver, described as vermeil where thickness and purity requirements are met, the exposed metal tarnishes rather than discolouring skin.
Stainless steel bases do not corrode, so worn areas simply look pale and grey rather than developing a reaction.
What extends the life of a plated piece
Skin oils, perfume, sunscreen and cleaning products all accelerate loss, so putting jewellery on last and removing it first makes a measurable difference.
Storing pieces separately prevents them abrading each other, which is a larger source of wear than most owners assume.
Replating is possible where the base is sound and the piece can be dismantled, and it is usually only economic on items with sentimental or design value.