Red Coral (Moonga)

Anybody buying Red Coral for the first time runs into the same wall. Two stones look alike, one costs ten times the other, and neither listing explains why. The answer is almost always treatment — what was done to the stone after it came out of the ground, and whether anybody mentioned it.

This page covers what Red Coral actually is, every treatment it commonly undergoes and what each does to the price, what gets sold in its place, what a laboratory report will and will not tell you, and how to look after it. Where something rests on tradition rather than on anything checkable, it is marked as such.

Red Coral, known in India as Moonga, is Calcium carbonate — organic, the skeleton of a marine animal. Its colour comes from carotenoid pigments. On the Mohs scale of hardness it sits at 3 to 4, which decides more about living with the stone than anything else does: how it should be cleaned, whether it can be worn daily, and what will damage it.

It is found in The Mediterranean, Japan, Taiwan, the Western Pacific. Where a stone came from affects its price in some varieties a great deal, and origin is a specialist laboratory determination rather than something a seller can simply assert.

This is the section to read if you read nothing else. Most coloured stone sold anywhere in the world has been treated, and that is not a scandal — it is ordinary trade, practised openly, and much of it is stable and accepted. The problem is never that a stone was treated. It is that the buyer was not told.

Two red corals can look identical across a counter and differ many times over in price on treatment alone. Here is what is done to red coral, and what each does.

Very common. Pale or white coral dyed red. Disclosable, and the dye can bleed or fade.

To improve polish and stability.

Powder bonded with resin and moulded. Sold as coral at low prices, and it is not the same thing.

A different, cheaper species dyed red. Extremely common.

Widespread.

Porous white stones that take dye readily.

A drop of acetone on an inconspicuous spot will lift dye from a dyed piece. Under magnification, genuine coral shows a fine wood-grain structure; bamboo coral shows visible growth rings and a coarser texture. Neither test is conclusive, but both are worth doing before a laboratory is worth paying for.

The trade judges coloured stone on four things, and they are not equally important however often they are listed in the same breath.

The largest factor by a long way among untreated stones. It has three parts: hue (the colour itself), tone (how light or dark) and saturation (how strong). Saturation is what people are really responding to when they say a stone has life. A dark stone and a pale one can both be poor for opposite reasons, and the range in between is where nearly all the price sits.

Colour is also the thing photographs lie about most. Ask for pictures in daylight and under ordinary indoor light, because some stones look quite different under each, and a seller who only ever shows one lighting condition is showing you the flattering one.

Clarity is judged by the standard for this stone, not by a general one. That matters here: red coral is a stone where inclusions are expected, and a clean example at a low price is the one to be careful about. Applying a diamond's clarity expectations to a coloured stone leads people to reject good material and buy treated material instead.

The least discussed and the most underrated. Cut decides how much of the colour you actually see: a well-cut stone returns light evenly across the face, a poorly cut one has a dead window in the middle where light passes straight through. Hold it over printed text — if you can read the words through the middle of the stone, it is windowed, and it will always look flatter than its colour grade suggests.

Quoted first almost everywhere and mattering least of the four. Price per carat rises with size rather than staying flat, so a two-carat stone costs a good deal more than twice a one-carat of the same quality — but a larger stone of poorer colour is worth less than a smaller fine one, whatever the weight says.

Working through it in this sequence avoids nearly every way this goes wrong.

Red Coral comes from The Mediterranean, Japan, Taiwan, the Western Pacific. For some varieties origin moves the price a great deal, and that is where a particular problem lives: origin is claimed far more often than the famous sources could possibly supply.

Origin determination is a specialist laboratory service, based on inclusion patterns and trace element chemistry, and it is not something a seller can simply assert. If origin is part of what you are paying for, the report has to say so — and it has to be a laboratory that offers origin determination, because not all of them do.

If origin is not part of what you are paying for, it is worth ignoring entirely. A fine stone from an unfashionable source is a fine stone.

Plenty of people arrive at this page holding a stone somebody gave them, or one they bought years ago before they knew what to ask. Having it checked is straightforward and costs far less than the stone did.

Any recognised gemmological laboratory will identify it, say whether it is natural, and name any treatment. You do not need to buy anything from anybody to have that done. If it turns out to be treated, or to be something else entirely, that is worth knowing — both for insurance and for the next time somebody offers you one.

A report identifies the material, says whether it is natural or laboratory-grown, names any treatment detected, and gives weight and measurements. That is a great deal, and for red coral it is most of what decides the price.

What it does not do is value the stone. Two red corals with identical reports can differ several times over on colour, cut and life, and no report will tell you that. Nor does a report vouch for anything the seller has added around it.

A larger stone of poorer colour is worth less than a smaller fine one, and weight is the easiest number for a listing to lead with. It is the least useful of the four things that decide price.

It identifies. It does not value. Those are different jobs and no laboratory does the second.

At a low enough price the stone is something else, or it is treated in a way nobody mentioned. Both happen far more often than a genuine bargain does.

More stones are damaged by ultrasonic cleaners and hot water than by anything else. See the care section below — it is specific to this stone and it matters.

Soft, porous and organic. Acids, perfume, sweat and cosmetics all attack it. Wipe with a damp cloth only. Never ultrasonic, never chemical cleaners. It will dull with wear, which is normal and can be repolished.

At 3 to 4 on the Mohs scale, red coral needs more care in a ring than in a pendant, where it is knocked less. That is worth settling before choosing a setting, because a setting is harder to change than a mind.

A bezel — metal wrapped around the girdle — protects the edges and suits softer stones and anyone who works with their hands. Prongs show more of the stone and let more light in, which matters for colour, but they expose the edges to knocks and they loosen over time. Have prongs checked once a year; a stone lost from a loose prong is the commonest way people lose a stone.

The metal affects the apparent colour more than most people expect. Yellow gold warms a stone and white metal cools it, and the same stone can look like two different grades in the two settings. Ask to see it against both before deciding.

Colour is the largest part of the price and the easiest thing to misrepresent with a camera. Saturation is routinely pushed in editing, and some stones look quite different in daylight than under shop lighting. Ask for pictures in both, and a short video, which is far harder to doctor convincingly than a still.

It is used to mean two different things and the difference is the whole transaction. Natural can mean not laboratory-grown, and it can be implied to mean untreated. A stone can be entirely natural and heavily treated at once. Ask about both separately, because a seller answering one question is not answering the other.

A report is worth what the laboratory behind it is worth. Some exist to produce paper rather than opinions. The test is simple: can you look the number up on their own site, and does the report name treatments as well as identifying the stone. A report that only identifies is telling you the easy half.

Stones cut to land exactly on a carat weight have usually been cut to hit the number rather than to show the stone. A little under a round weight often costs noticeably less for a stone that looks the same size, because the market prices the number rather than the millimetres.

Metal, finger, day, weight, what is said, what is avoided. Specific enough to follow without writing to ask.