What Turns Gold Plated Jewelry Black

A chain goes into a drawer in August and comes out in November with a shadow on it. Not dirt, exactly. The links near the clasp have gone a gray-brown that is hard to name, and the ones that lay in the fold of the pouch are still bright. Nobody wore it. Nobody spilled anything on it. It darkened in the dark, on its own schedule.

A soft cloth brings most of it back the first time. Less the second time. Somewhere around the third the piece quietly stops being something you reach for, and it is never a decision, only an accumulation of mornings where something else was easier.

One clarification first, because the phrase on the label does more work than it was built for. Gold plated describes a surface. 18K gold plated describes the color of that surface. Neither describes how much gold is in your hand, and the second one is read by almost everybody as if it did.

Which leaves the question people actually ask, in the form they ask it: if the outside is gold, why is it going black? Gold does not go black. That is the whole of the puzzle, and also the start of the answer.

A plated piece in cross-section. The gold is a coating measured in tenths of a micron, drawn here about fourteen times thicker than it is, over a base metal that behaves nothing like it.

The gold on a plated piece is a coating, and a thin one

A plated piece is a stack. At the bottom is a base metal, usually brass or sterling silver, occasionally steel. Above that there is often a thin barrier layer, nickel or palladium, whose job is to keep the base from migrating upward. On top is the gold, deposited electrically, and it is the only part you ever see or touch.

The thickness of that top layer is where the language stops being intuitive. Under the FTC's jewelry guides, a piece may be called gold electroplate when the coating is 10 karat or better and at least 0.175 microns thick. That is roughly seven millionths of an inch, thinner than a sheet of household plastic wrap by a wide margin. Heavy gold electroplate asks for 2.5 microns, about fourteen times more. Vermeil, under a separate section, requires a sterling silver base plus a gold layer of 10 karat or higher at 2.5 microns or more.

Those are floors, not descriptions, and the distance between the floor and a good coating is enormous. Two pieces can carry the same four words on the tag and differ by a factor of ten in what is actually on them. Nothing on the label separates them. You find out by wearing them.

So 18K gold plated tells you the karat of a film, not the composition of an object. It is a color specification. It is not wrong, and it is not a lie, and it is also not the thing most people believe they are being told.

Gold does not tarnish. What sits under it does

Pure gold is about as chemically indifferent as metals get. It does not rust and it does not tarnish, and a solid gold alloy inherits most of that indifference from the gold in it. Whatever is turning dark on a plated chain is not the gold. It is the metal underneath, arriving at the surface.

It arrives by two routes, and both are ordinary. The first is porosity: an electroplated film a few tenths of a micron thick is not the continuous skin it appears to be at arm's length. It carries microscopic pores. Air, moisture and whatever is dissolved in them reach the base metal through those openings, and the reaction product spreads back out across the surface from each one.

The second is thinning. Plating does not go on evenly. Current density is higher at edges, corners and raised areas during the plating bath, and the coating there is thinner from the day it was made. Then wear takes over: the places that rub against skin, cuff, keyboard edge or another piece of jewelry lose the film first. On a ring it is the shoulders. On a chain it is the links that sit against a collarbone.

What the base metal does once it is reachable depends on what it is. Sterling silver forms silver sulfide, which is the black on your grandmother's flatware. Brass and other copper alloys form copper sulfides and oxides, which read browner. Either way the trigger is usually sulfur, and the sources are household: eggs, onions and garlic, wool and some other protein fibers, rubber, certain adhesives and papers, and the sulfur compounds in ordinary air, which are higher in cities than the word air suggests. Sweat supplies chloride and acid, which does its own separate damage. None of this is exotic, and none of it is avoidable by being careful.

A piece kept in a drawer is not a piece kept safe

The version of the question that deserves more attention than it gets is the one about the piece that hardly left its box. Not wearing something is not the same as not exposing it, and storage introduces a set of problems that wearing does not.

A sealed bag seals whatever was already inside it. Humid air, the last of a hand cream, a fingerprint. A pouch or a lined box that smells faintly of rubber is usually telling the truth about its contents. Rubber bands and many foam inserts release sulfur compounds continuously and slowly, and a small enclosed volume concentrates them. Untreated cardboard and some papers do a gentler version of the same thing. Warmth speeds all of it, which is why a drawer against a sunlit wall or above a radiator is worse than a cool one, for reasons that have nothing to do with light.

And pieces stored loose against each other abrade each other. The coating comes off at the contact points, in the dark, without anybody wearing anything. A chain that tarnished in storage is not a mystery. It is a record of the container.

Four ways the same band goes dark. The pattern is usually more informative than the fact, and most pieces show more than one at once.

The pattern of the black says where it came from

“It lost its color” is too coarse a description to act on. Where the darkening sits tends to say which of the mechanisms above is running.

Scattered spots on an otherwise clean flat surface point at porosity or at something that landed on it: a drop of a product, a fingerprint left on over a weekend. The pattern is random because pores are random.

Darkening concentrated on edges, corners, raised ornament and the high points of a texture points at thickness. Those are the places the coating was thinnest to begin with and the first places wear takes it off. If a piece is bright in its recesses and dark on its ridges, that is not chemistry finding a favorite, that is the film being gone in the obvious places.

A broad, even dullness across the whole piece, recesses included, points at the environment it has been sitting in rather than at anything you did to it. This is the drawer pattern.

Color change only where it touches skin, and cleanly bright everywhere else, points at you: sweat chemistry, a lotion, a medication, a climate. Skin varies more than people expect, and two people can wear the same piece with different results and both be normal.

Care postpones one of these and restores the other

The practical advice is short, and it is the same advice for both constructions. Put jewelry on last, after perfume, sunscreen, hairspray and lotion have dried, and take it off first, before a shower, a swim, a workout or dishes. Wipe a piece with a dry soft cloth before it goes away, because the film left by a day of wear is what reacts overnight. Give each piece its own pouch or compartment, away from rubber, away from heat, and let a little air reach it rather than sealing it wet.

What changes is what that care is buying. On a plated piece, care is a delay. The coating has a finite thickness, and every cleaning, every polish, every pass with a cloth removes a fraction of it. Polishing a plated piece that has already worn through makes it worse, because the only thing you can remove is the gold that is left. The piece is not being restored. It is being spent more slowly.

On solid gold the same care returns the object. There is no layer to lose, because the alloy at the surface is the alloy all the way down. A scratch in solid 14K gold exposes more solid 14K gold. A jeweler polishes it out and the piece is the piece again. This is the entire practical difference, and it does not show up in a photograph or in the first month of wearing.

One identical scratch, two constructions. On a plated piece it opens a route to a reactive metal; on solid metal it reaches more of the same alloy.

The stamp inside is what tells you which object you are holding. 14K, 18K, 585, 750, PLAT or 950 mark solid metal. GP, GEP, HGE, GF, 1/20 12K GF or 925 with a gold-colored surface mark a coating over something else. It takes five seconds and a phone camera, and it settles the question that the product page was never quite going to answer. Everything we make is solid, which is why the question of 14K against 18K comes up on our pages and the question of plating does not.

Where this argument works against us

Two things ought to be said plainly by anyone making the case above.

The first is that we use a coating too. White gold is a yellow alloy made pale, and nearly all of it is finished with rhodium, which is a plating a fraction of a micron thick. It wears, exactly as any plating wears, most quickly on the underside of a ring shank — the part of a piece like this solid 14K white gold solitaire that spends the day against a desk. When it thins, a warmer tone shows through, and the fix is re-plating every few years. That is a real maintenance obligation and it belongs in the open, which is part of why platinum and white gold are worth separating before choosing. Solid platinum carries no such coating; it grays into a patina instead of losing a layer.

The second is that solid gold is not inert. It is gold alloyed with copper, silver and other metals for hardness and color, and those companions respond to sulfur and chloride like any other. Solid 14K has more of them than solid 18K, which is one reason the two behave differently on skin over years. A solid gold chain can develop a dull film in a sulfurous drawer. The difference is that the film sits on the surface of the same metal that is underneath it, so cleaning it is recovery rather than subtraction.

And plated jewelry earns its place. For a shape you want to try once, for a trend with a known expiry, for a piece that will be worn hard in conditions no one should ask fine jewelry to survive, a coating is the sensible construction. The failure is not the material. The failure is buying it under the impression that it is the other thing, and then reading its ordinary behavior as a defect.

The chain in the drawer did what it was built to do, for as long as it had to give. What went wrong was upstream of the tarnish: a word on a tag that described a color and was heard as a promise about substance. Nothing about the black is a betrayal, and no amount of care was going to change the arithmetic of a film a few millionths of an inch thick.

The useful question is not how to keep a coating from wearing. It is which pieces you want to still own in ten years, and those are worth buying in metal that goes all the way through. The rest can be a coating, knowingly, with an end date you set yourself. If the decision rather than the mechanism is what you are weighing, plated against solid, compared on cost, lifespan and repair is the piece to read next. We are happy to read a stamp off a photograph if you are not sure which one you have.

Sources - FTC, Jewelry Guides, 16 CFR § 23.3 — Misrepresentation as to gold content, including the terms “gold filled,” “gold plate” and “gold electroplate” — https://www.ecfr.gov/current/title-16/chapter-I/subchapter-B/part-23/section-23.3 - FTC, Jewelry Guides, 16 CFR § 23.4 — Misuse of the word “vermeil” — https://www.ecfr.gov/current/title-16/chapter-I/subchapter-B/part-23/section-23.4