Listen to this guide
- Silvering is the metal layer on the back of the glass that gives you a reflection. It is what fails first in a poorly made mirror — usually long before the glass itself.
- NZ coastal homes are hard on cheap mirrors. Salt-laden air, bathroom humidity, and unsealed backings combine to corrode the silver layer from the edges inward — the classic "black creeping in from the corner" you have seen on older mirrors.
- The fix is spec, not maintenance. Double silver copper-free coating on a sealed backing is the combination that survives coastal Auckland, Wellington wind-rain, and any NZ bathroom for decades, not years.
You have probably seen it. A mirror that has lived in a bathroom or a coastal home for a few years starts to grow a dark stain creeping in from the corners. The reflection in the middle is still fine, but the edges go blotchy and grey. That is not the glass failing. That is the silvering failing. And in NZ, where most homes are within a 50 km strike of saltwater and many bathrooms swing from 40% to 95% humidity inside a single shower, it is the most common way a mirror dies.
This guide explains in plain language what silvering actually is, the four ways it fails, why coastal NZ homes are uniquely tough on it, and the three spec lines worth asking about before you buy any mirror you want to keep for more than a year or two. If you have already decided what to buy and just want the spec checklist, jump to the checklist near the bottom. Otherwise, start at the beginning — the chemistry only takes two minutes and the rest of the article makes more sense once you have it.
What does "silvering" actually mean?
A modern mirror is a sandwich. From the front, looking at your reflection, what you see is: a sheet of glass, a microscopically thin layer of reflective metal painted onto the back of the glass, then one or more protective coats sealing that metal layer against moisture and air. Light passes through the front of the glass, hits the metal layer, bounces back, and reaches your eye. That metal layer is doing all of the visible work, and it is what manufacturers mean when they talk about "the silvering."
The metal is usually silver, applied as a liquid silver-nitrate solution which is then chemically reduced into a metallic film about 80 to 120 nanometres thick. Silver is used because it reflects the widest range of visible light with the least colour shift — a silver mirror gives you a bright, neutral reflection. Some budget bathroom and utility mirrors use aluminium instead. Aluminium is cheaper but reflects slightly less light and shifts the reflection a fraction cooler. Most quality NZ full length mirrors use silver.
Behind the silver, the protective layer is the part that earns its keep. In a traditional single silver mirror the silver is sealed first with a thin layer of copper, then two coats of waterproof paint. The copper is there as a sacrificial barrier — it oxidises before the silver does, buying the silver some time. In a modern double silver copper-free mirror the copper is gone entirely; instead, two layers of silver are sealed directly with lead-free paint. With nothing soft for moisture to find, there is nothing to corrode first.
So when someone says "silvering quality" they almost always mean two related things: how much silver is on the back of the glass, and what is protecting it. Get either of those wrong and the reflection you bought today will be tarnished and edge-blotched in four or five years.
The four ways silvering fails (and what each one looks like)
Mirror failures look surprisingly similar across brands and price points. There are really only four common modes and each one tells you something specific about what went wrong with the spec.
1. Edge desilvering (the "black creeping in from the corners" look)
This is by far the most common NZ mirror failure. Dark grey or black blotches appear at the edges and corners and grow inward over months and years. The reflection in the centre stays bright, but the edges go blotchy and uneven.
Cause: moisture has worked its way in through the back-paint at the edges and reached the silver (or, in a single silver mirror, the copper layer behind it). Once the copper oxidises, the silver above it loses its bond and starts to lift. The damage is irreversible — there is no home remedy that restores a desilvered edge.
What it tells you about the spec: the back-paint was thin, the edge was unsealed, the room was humid, or all three at once. In coastal NZ homes, salt-laden air accelerates this dramatically — chloride ions are aggressive towards both copper and silver, and they ride humidity through any gap they can find. A cheap single silver mirror near a Tauranga or Mt Maunganui beach can show edge desilvering inside a single year.
2. Black-spot tarnish (random dark spots across the face)
Less common but distinctive: small dark spots, often circular or irregular, appearing not at the edges but scattered across the face of the mirror. Sometimes called "fly spots" because the older folklore blames insects.
Cause: tiny pinhole defects in the back-paint that let moisture reach the silver in isolated spots. Each pinhole becomes a corrosion site. Cheaper paint applied too thin is the usual culprit; sometimes a manufacturing defect in the silvering chemistry itself leaves microscopic voids that fail later.
What it tells you about the spec: the back-paint is sub-spec or applied too thinly. A quality mirror uses two coats of waterproof, lead-free paint that completely seals the silver layer.
3. Peeling and lifting (large areas of silver detaching)
The most catastrophic failure. Large patches of silver detach from the glass and lift away, often visible as opaque pale or grey blotches behind the reflection. Sometimes the silver curls away from the glass entirely.
Cause: usually a bonding failure between the silver and the glass — either because the glass was not properly cleaned before silvering, or because the mirror has been exposed to harsh chemicals. Common harsh chemicals that destroy silvering: ammonia-based cleaners (yes, Windex), citrus cleaners, vinegar in any concentration above household-rinse, and anything containing chlorine.
What it tells you about the spec: this is almost always either a manufacturing defect (sub-spec bonding chemistry) or a maintenance mistake (wrong cleaner). The fix is the same either way: buy a quality mirror from the start and clean it with a damp microfibre cloth and a drop of dish soap, nothing else.
4. Oxidation haze (overall dulling of the reflection)
The most subtle. The mirror does not develop spots or edge-blackening — it just looks slightly less bright than it used to. The reflection feels flatter, slightly grey, the way an old chrome bumper looks compared to a new one.
Cause: slow oxidation of the silver layer through a sub-spec backing that is technically intact but lets a small amount of moisture through over years. The silver does not corrode dramatically; it slowly dulls.
What it tells you about the spec: low-end silvering on a bargain backing. Quality double silver mirrors hold their initial brightness for decades because the copper-free chemistry simply has nothing easy to oxidise.
Why NZ coastal homes are harder on mirrors
NZ is a long, narrow country. Auckland sits on a thin isthmus between two coasts. Wellington has the Cook Strait at its doorstep. Christchurch faces the Pacific to the east and the Southern Alps to the west, drawing constant cross-currents of moist air. Nelson, Tauranga, the Bay of Islands, the Coromandel — almost every meaningful population centre is within an easy walk of the sea. That matters for mirrors more than people realise.
The reason is something atmospheric chemists call marine aerosol. Wind picks up microscopic droplets of seawater, the water evaporates as the droplets travel inland, and what is left behind is a fine particulate of salt — primarily sodium chloride, plus traces of magnesium and other ions. That salt rides the prevailing winds for kilometres inland. It settles on every horizontal and vertical surface, including the back edges of mirrors hanging on walls inside otherwise well-sealed homes.
Salt is hygroscopic — it actively pulls water vapour out of the air. So once salt deposits build up on the back-edge of a mirror, they create a small permanent reservoir of moisture exactly where the silvering is most exposed. Add in NZ bathroom humidity swings (a hot shower takes a room from 40% to 95% relative humidity in five minutes) and you have a perfect attack surface for chloride-driven corrosion.
This is not theoretical. North Shore Auckland, the Coromandel, Mt Maunganui, Lyall Bay in Wellington, Sumner in Christchurch — any home within roughly 2 km of an open coast is in the marine-aerosol band. We have refurbished bedrooms in Whangaparāoa where the previous owner's mirrors developed visible edge corrosion inside two years; in the same homes, mirrors with double silver copper-free backings are still pristine after five.
Bathrooms: the second front
Bathrooms are the second great mirror killer in NZ homes, and the mechanism is different from coastal salt. The problem here is the humidity swing, repeated daily. A hot shower releases water vapour at close to skin temperature. That vapour condenses on every cooler surface in the room, including the back of any mirror that is not perfectly sealed against the wall. Over hundreds of cycles a year, that condensation finds its way to the edges of the silvering and starts the same corrosion process as coastal salt — just slower and more localised.
The fixes are a combination of spec and installation. Spec-side: double silver copper-free glass on a sealed backing. Installation-side: a small air gap between the mirror back and the wall (rather than glued flush) and adequate room ventilation. The mirror itself can be excellent quality and still fail prematurely if it is glued flat to a wall behind which moisture pools.
One more bathroom note. Heated bathroom mirrors (the ones with a demister pad on the back) work brilliantly against fog but they also keep the back of the mirror slightly warm, which can actually accelerate corrosion if the silvering itself is sub-spec. The fix is the same: a quality silver layer in the first place. A demister pad on top of a budget mirror is a short-term win and a medium-term loss.
Can you repair a mirror that has already desilvered?
Honest answer: not really. There are DIY kits sold online that claim to re-silver a mirror, and there are specialty restorers in larger cities who can re-silver antique mirrors at considerable expense. For a modern wall or full length mirror that has developed edge corrosion, replacement is almost always the more sensible call. The cost of professional re-silvering on a modern mirror frequently exceeds the cost of a new quality mirror, and DIY kits rarely give a result that holds up.
The practical move when you see edge corrosion starting: do not panic, but plan a replacement. Edge desilvering is a slow process — once it starts, you typically have a year or more before it becomes intrusive in the reflection. That is enough time to budget for a quality replacement rather than a panic-buy. When you do replace, the spec checklist below tells you what to look for so the next mirror is the last one.
The three spec lines worth asking about
If you read no other section of this article, read this one. Before buying any mirror you intend to keep for more than a few years — and especially before buying any mirror for a bathroom, laundry, kitchen, or coastal NZ home — confirm these three things in writing.
| Spec to ask about | What "good" looks like | What "bad" looks like |
|---|---|---|
| Silver coating type | "Double silver, copper-free, lead-free paint backing" | No mention of silvering at all, or vague "high reflectivity coating" |
| Backing material | "Sealed MDF or aluminium composite backing" | "Cardboard" or "paper" backing, or no specification given |
| Glass thickness + iron content | "5mm low iron glass" (clarity + flatness) | "3mm" or "4mm" thickness, or no iron-content specification |
That is the entire spec literacy you need. Three lines. If a product page or a retailer cannot give you straight answers on those three points, it is almost always because the answers are not the ones they want to lead with — and that tells you what kind of mirror you are looking at.
Two don't-do-this NZ-specific warnings
Do not hang a mirror in direct afternoon sun for years on end. UV does not directly damage the silvering, but it heats the glass, which expands and contracts the back-paint daily. Repeated expansion-contraction cycles open microscopic gaps in the paint that moisture finds. A north-facing or west-facing wall that catches strong NZ afternoon sun is a faster-ageing position than a south-facing or interior wall.
Do not glue a mirror flush to a bathroom wall. Always leave the small air gap that the manufacturer's brackets or French cleats create. A flush-glued mirror traps any moisture that does reach the back, which is the slowest possible drying environment and the fastest possible corrosion environment.
Why every C&F Creation mirror uses the premium spec
For full transparency: every full length mirror we make uses 5mm low iron glass with a double silver copper-free coating on a sealed MDF backing. We made that decision early because NZ is a hard country for mirrors. A buyer in Whangārei, Tauranga, Wellington, Christchurch or Bluff is almost always in the marine-aerosol band, and even an inland Hamilton or Cambridge bathroom puts a mirror through hundreds of humidity cycles a year. Building to a single premium spec rather than a budget and a premium tier means we never have to ask which environment the mirror is going into.
4.94 stars from 195+ reviews. Afterpay available at checkout. NZ wide delivery via Mainfreight at live rates calculated at checkout. NZ Owned. Mirrors are NZ designed and built to last NZ humidity and coastal conditions.
Browse every C&F full length mirror
All built with 5mm low iron glass, double silver copper-free coating, and sealed backings — for NZ homes, coast and country.
Shop Full Length Mirrors Use the Size CalculatorRelated reading
- Single silver vs double silver vs low iron mirror glass — the buyer comparison (the spec choice if you are deciding which to buy)
- Behind the scenes — low iron glass, reflective coatings, and why thickness matters (deeper dive on the clarity axis)
- Mirror distortion — why your reflection looks wavy and the 60 second test (the flatness side of mirror quality)
- Why you look different in different mirrors (perception, lighting, viewing angle)
- How to choose a high quality full length mirror (a broader buying guide)
Frequently asked questions
What is mirror silvering in plain language?
Silvering is the thin layer of reflective metal — almost always silver, occasionally aluminium — painted onto the back of a mirror's glass. It is the part that gives you a reflection. The glass in front protects it and the paint behind it seals it from the air. When a mirror "fails" it is almost always the silvering that has corroded, not the glass that has broken.
Why do mirrors go black at the edges over time?
The black creeping in from the corners is edge desilvering. Moisture has worked its way in through the back-paint at the edge of the mirror, reached the silver layer (or the copper layer beneath it in a single silver mirror), and started corroding it. It is by far the most common mirror failure in NZ — accelerated dramatically in coastal homes by salt-laden air and in bathrooms by repeated humidity cycles. The damage is irreversible.
Does coastal salt air really damage mirrors?
Yes, and it is one of the strongest mirror failure factors in NZ homes. Marine aerosol — microscopic salt particles carried inland by coastal wind — settles on the back edges of mirrors and pulls water vapour out of the air, creating a constant moisture reservoir against the silvering. Any home within roughly 2 km of an open coast is in the marine-aerosol band, which covers most of Auckland, Wellington, Tauranga, Christchurch, and Nelson. Spec the mirror for coastal conditions even if you live further inland than a beachfront house.
Does a bathroom mirror need a different spec than a bedroom mirror?
Yes. Bathroom humidity swings from around 40% to 95% relative humidity during a single shower, repeated daily. That cycle is the slow killer for budget mirrors. A bathroom mirror should be double silver copper-free on a sealed MDF or aluminium-composite backing, installed with a small air gap between the mirror and the wall so the back is not glued flush to a damp surface. A quality bedroom mirror in a dry, well-ventilated room can be slightly less rigorously spec'd, but double silver is still the safer call for a long-term piece.
Can a mirror with edge desilvering be repaired?
In practice, no — at least not in a way that makes financial sense. There are specialist re-silverers in larger NZ cities who can restore antique mirrors, but the cost typically exceeds the cost of a new quality modern mirror. DIY re-silvering kits rarely produce a result that holds up. If you see edge corrosion starting on a mirror you care about, plan a replacement over the next year or two rather than attempting a repair. Use the time to spec the replacement properly so it is the last mirror that room needs.
What cleaner is safe to use on a mirror without damaging the silvering?
A damp microfibre cloth with a drop of plain dish soap, finished with a dry microfibre cloth. Avoid ammonia-based cleaners (including most blue glass cleaners), citrus-based cleaners, vinegar in any concentration above household-rinse strength, and anything containing chlorine. Those chemicals can creep around to the back of the mirror and attack the silvering directly. Always wipe the mirror, never spray cleaner onto the mirror — spray drift gets onto the edges where the silvering is most exposed.
Written by the C&F Creation Team. C&F Creation is an NZ Owned mirror and lighting business. Mirrors are NZ designed, built with 5mm low iron glass, double silver copper-free coatings, and sealed backings, and shipped NZ wide via Mainfreight at live rates calculated at checkout. Afterpay available.
