Moissanite 101
Why Cubic Zirconia Goes Cloudy
It does not cloud. Nothing forms inside it and nothing gets in. The surface is simply worn away by something in every room you have ever been in.
Written by the Mapple Gems workshop, Surat Β· Updated 24 August 2026
Short answer
Cubic zirconia sits at Mohs 8.25β8.5, and household dust contains quartz at Mohs 7. Ordinary handling therefore abrades it: the crisp facet edges round off and the polished surfaces micro-scratch, so light scatters instead of reflecting. The stone is not cloudy on the inside β its outside has been sanded, and it cannot be restored economically.
"Cloudy" is the word everyone uses and it is the wrong one, which matters because it points at the wrong explanation. People assume moisture got in, or soap built up, or the stone was low quality to begin with. None of those is what happened.
What a faceted stone is doing
A cut stone returns light because of two things: flat, polished facet surfaces that reflect cleanly, and sharp facet junctions where those surfaces meet. Crisp junctions produce defined flashes. Rounded junctions blur them into a general glow.
So there are two ways to ruin the optics without touching the inside of the stone at all: dull the surfaces, or round the edges. Abrasion does both, and it does the edges first, because an edge presents less material to whatever is rubbing against it.
The abrasive is dust
Household dust contains quartz particles. Quartz is Mohs 7 β it is one of the commonest minerals on the planet and it is on every surface you touch.
Cubic zirconia at 8.25β8.5 is above quartz, which sounds like enough. It is not, for two reasons. The Mohs scale is ordinal rather than linear, so the real gap between 7 and 8.5 is far smaller than it reads. And the contact is not occasional β it is thousands of small events across years of ordinary wear.
The effect is cumulative and directional: facet junctions round first, then the flat surfaces micro-scratch, then the whole stone reads soft and greyish. Nothing dramatic ever happened to it.
| Material | Mohs | Effect of quartz dust at Mohs 7 |
|---|---|---|
| Lab grown diamond | 10 | None |
| Moissanite | 9.25 | None |
| White sapphire | 9 | Slow softening of polish |
| Cubic zirconia | 8.25β8.5 | Edges round, surfaces scratch |
| White topaz | 8 | Same, faster |
| Gold setting | ~2.8 | Marks from the first week β unavoidable |
The five-minute test
Before assuming the surface has gone, rule out the far commoner explanation. A stone can look dull because there is a film on the pavilion β sunscreen and hand cream are the two main culprits, and they collect on the underside where no cloth reaches.
Warm water, a drop of washing-up liquid, five-minute soak, soft toothbrush worked from underneath through the gallery, rinse in a bowl rather than over a drain, dry fully. Brushing the top does nothing, because a faceted stone returns light through its pavilion and that is where the film sits.
If it comes back bright, it was dirt. That happens on any material and is free to fix.
If nothing changes, the surface has been abraded. That is not reversible by cleaning, because there is nothing on the stone to remove β material has been taken off it.
From our bench in Surat
We do not set cubic zirconia, so we have no commercial reason to be generous about it β which is why it is worth saying that CZ is a genuinely good material for what it is actually for. As a costume or occasion stone worn a few times a year, it looks excellent and it will keep looking excellent, because the abrasion clock only runs while it is being worn. The failure is not the material; it is putting an occasion stone into daily service.
We see the same failure with real fine jewellery all the time. A piece built for perhaps a hundred wearings gets a thousand in three years, and the repairs land around year four. CZ is that pattern in a stone rather than a setting.
Can it be repolished?
Technically a stone can be recut and repolished. Whether it is worth doing is a different question.
Recutting means unsetting the stone, removing material to establish fresh surfaces and sharp junctions, then resetting it. On a sapphire that can make sense, because the material has value. On cubic zirconia the bench labour costs several times the replacement stone, so nobody does it.
Replacing a CZ is straightforward if the setting is sound. Worth noting: whoever unsets and resets it should check the prongs while the stone is out. If a stone has been in place long enough to dull, the prongs have had the same years of wear.
Slowing it down
- Treat it as occasion jewellery. That single decision does more than everything below combined.
- One pouch per piece in storage. Most abrasion damage happens in a jewellery box, not on a hand β harder stones score everything they touch through years of small movements.
- Take it off for cleaning, gardening and the gym.
- Never use a polishing cloth habitually β those are mildly abrasive by design.
- Never toothpaste. It is an abrasive, and against gold at Mohs 2.8 it is working on the setting as much as the stone.
- A bezel setting shelters the girdle and the facet edges nearest it β worth specifying for any softer stone.
Keep reading
Which diamond alternative survives daily wear
Frequently asked questions
Why does cubic zirconia go cloudy?
It does not cloud internally. At Mohs 8.25β8.5 it is abraded by quartz particles in ordinary household dust, which sit at Mohs 7. The sharp facet junctions round off and the polished surfaces micro-scratch, so light scatters instead of reflecting cleanly.
Can a cloudy cubic zirconia be cleaned back to new?
Only if the dullness is film rather than abrasion. Soak in warm water with a drop of washing-up liquid for five minutes and brush from underneath. If it comes back, it was dirt. If nothing changes, material has been removed from the surface and cleaning cannot restore it.
Does moissanite go cloudy in the same way?
No. At Mohs 9.25 it is far enough above quartz that ordinary dust does not abrade it. When a moissanite looks dull it is almost always film on the pavilion from sunscreen or hand cream, which a five-minute soak removes.
How long does a cubic zirconia last?
It depends entirely on wear rather than age, because the abrasion clock only runs while the piece is being worn. In daily wear the change is usually visible within a few years; worn a handful of times a year it can look excellent for a very long time.
Is it worth repolishing a dulled stone?
On sapphire it can be, because the material has value. On cubic zirconia the bench labour costs several times a replacement stone, so replacement is the practical answer. Have the prongs checked while the stone is out β they have had the same years of wear.
Nothing we set is softer than 9.25
Moissanite and lab grown diamond only, made to order in our own Surat workshop.
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