How long does the colour last?

Search "waterproof jewelry" and you will find a hundred brands making the claim and almost none explaining it. Two different things get mixed together: whether the steel corrodes, and whether the colour survives. They have different answers, and only one of them is impressive.

The steel does not tarnish. That part is chemistry.

Stainless steel is an iron-chromium alloy that protects itself. Chromium at the surface reacts with oxygen to form a passive oxide layer a few atoms thick, and if that layer is scratched, it re-forms within minutes in air. This is why stainless steel does not rust the way ordinary steel does, and why a piece worn daily does not develop the green or black staining that plated brass produces.

That property belongs to the alloy, not to the finish, and it is true of both 304 and 316L. 316L adds molybdenum, which improves resistance to chlorides — that is why the earring posts and ring interiors we make are 316L more often than not.

So the surprising part of the claim is not the steel. It is the colour.

The colour is the part that can fail

A bare stainless steel piece cannot lose its colour, because it has none — the metal is grey-white throughout. Colour comes from a coating, and a coating is the only part of the piece that can wear away.

That is why the finish choice decides the durability claim, and it is the one specification worth arguing about with a supplier:

• PVD over stainless steel. The colour layer is a ceramic compound grown into the surface in a vacuum chamber. It does not flake, it does not sit on top of a soft metal deposit, and there is no plating layer for sweat to attack. This is what we use for every coloured piece we produce.
• Electroplating over brass or zinc. A softer metal layer deposited on top of a metal that corrodes underneath. It wears at high points, and once breached, the base metal starts to oxidise through the remaining layer — visible as dark staining on brass and white oxide on zinc.
• Electroplating over stainless steel. Better than over brass, because the base does not corrode. But the colour is still a soft deposit that abrades at the high points, and the piece loses tone long before a PVD-coated one.

What PVD-coated steel survives in practice

In ordinary wear — showering daily, sweating, wearing a ring to the gym, swimming in a pool or the sea, spraying perfume near a necklace — PVD-coated 316L holds its colour. This is based on what our buyers report over multi-year use of repeat orders, not on a controlled wear test, and we are careful to say so.

What does eventually abrade it:

• Sustained mechanical friction against a hard edge. A bangle worn against a desk all day, a chain rubbing a seatbelt strap, keys in the same pocket as a ring. This is the dominant wear mechanism, and it has nothing to do with water.
• Chlorinated water over long exposure. Pool chemicals are aggressive to thin films in a way that seawater is not. Occasional swimming is fine; training in a pool every day for years is a harder life for any coating.
• Abrasive cosmetics. Scrubs, exfoliants and some sunscreens are physically abrasive. A piece worn under a gritty product wears faster than the same piece worn on clean skin.
• Damage from repair. Sizing a ring or re-polishing a scratched surface can cut through a coating locally. That is a real limitation and worth knowing before you buy a coated piece in a size you may need to change.

Why nobody should give you a number of months

A brand that promises "colour guaranteed for 24 months" is either testing under a fixed protocol that does not resemble real wear, or absorbing the returns.

Coating life depends on the wearer, not only on the piece. The same bracelet worn by a jeweller who takes it off at her desk and by a builder who never removes it will look different after a year, and both are normal use. A number in months would be a marketing figure, not an engineering one.

What a factory can control is the specification, and that is what should be in writing on a quote:

• Base alloy — 304 or 316L, stated explicitly.
• Surface preparation — polish grade before coating. Coating over a poor polish fails fast regardless of coating quality.
• Coating process and thickness — PVD at a stated micron range, not "advanced technology".
• Colour reference — a retained approved piece to match reorders against.

Ask for those four and you can compare two suppliers meaningfully. Ask for "how many months" and you will get a number that sounds reassuring and means nothing.

What to put on your product page

If you are selling this jewelry, the safe claims are the ones that describe the mechanism rather than a duration:

• "Waterproof" — defensible for PVD-coated stainless steel. It does not corrode in water.
• "Tarnish-resistant" — defensible, because the steel does not tarnish and the coating does not oxidise.
• "Sweat-proof" — defensible, and it is the claim that matters most to everyday-wear customers.
• "Scratch-proof" — not defensible, for any coated piece. "Scratch-resistant" is honest; "proof" is not.
• "Lifetime colour guarantee" — a business decision, not a materials claim. If you offer it, price the returns into the product.

The strongest position for a brand is not the loudest claim. It is the one you can explain when a customer asks how it works — because the customer who asks is the one who is about to spend money.