Recognising Real Coral: Red Coral, Dyed Bamboo, Plastic and Glass
Precious coral is the skeleton of a marine animal. Red coral, dyed bamboo coral, resin and glass: pointers, safe tests and questions of protection.
Key points
| Nature | calcium carbonate skeleton of a marine animal: an organic material |
|---|---|
| Hardness (Mohs) | about 3.5: soft |
| Classic species | Corallium rubrum, mainly in the Mediterranean |
| Other precious corals | species from the western Pacific (Japan, Taiwan), often paler |
| Common treatments | bleaching, dyeing, impregnation with wax, oil or resin |
| Common imitations | dyed bamboo coral, plastic, glass, reconstituted powder |
| Protection | regulated fishing in the Mediterranean; some corals are listed under CITES |
| Test to avoid | acid: coral reacts to it and is destroyed |
What precious coral is
Precious coral is neither a mineral nor a rock: it is the skeleton of a colonial marine animal, made mostly of calcium carbonate coloured by pigments (carotenoids). Its hardness is about 3.5 on the Mohs scale. The living colony is white; it is the red, orange or pink skeleton that is cut. The classic species is Corallium rubrum, which lives in the Mediterranean between a few metres and several hundred metres deep. Other species live in the western Pacific, around Japan and Taiwan, often at great depths.
Coral has been worked since antiquity, notably in Naples, Torre del Greco and Genoa. It is soft: it is carved into cabochons, beads and branches.
What is sold as “coral”
- Natural precious coral (Corallium), polished or lightly worked.
- Treated coral: bleached, dyed to even out the colour, impregnated with wax, oil or resin.
- Dyed bamboo coral: a different kind of coral, with a segmented skeleton, naturally white and very often dyed red or pink to imitate precious coral. It is legitimate when sold as "dyed bamboo coral".
- Reconstituted coral: coral powder bound together with resin.
- Imitations: plastic, resin, glass, sometimes dyed marble or shell.
- White reef coral (white decorative branches, madrepores): this is something else, the skeleton of reef-building corals, unrelated to precious coral and protected.
The word "coral" alone covers many situations. The description must say which species it is and whether the colour is natural or obtained by dyeing.
Warning signs
| Sign | Natural precious coral | Dyed bamboo coral, plastic or glass |
|---|---|---|
| Surface | Fine parallel striations along the length of the branch, small pits, a wavy pattern | Plastic and glass: smooth surface with no structure; bamboo: white or black segments (nodes) |
| Colour | Red, orange or pink, sometimes slightly varied depending on the area | Red that is too uniform; colour concentrated in cracks and around the drill hole |
| Weight and feel | Cool, relatively dense | Light, warm plastic; colder, heavier glass |
| Shapes | Irregular branches, beads of slightly varied size | Identical beads, moulded, sometimes with a moulding line |
| Price | High for good-quality red coral | Very low for large beads or long branches |
Bamboo coral is recognised by its fine lengthwise stripes and regular nodes: on a dyed tube, regular white or black junctions are typical.
Simple, safe tests
- Read the description: "red coral from the Mediterranean", "dyed bamboo coral", "reconstituted coral", "imitation".
- Look under the magnifier: fine, irregular striations parallel to the axis are natural. A grain that is too regular, bubbles or a moulding line are artificial.
- Look at the drill hole: accumulated dye, a white core under a surface colour, or a painted layer that flakes all indicate dye or coating.
- Weigh and feel: plastic is lighter and warms quickly.
- Rub a damp white cotton pad (lukewarm water) on an inconspicuous spot: colour on the cotton indicates poorly fixed dye.
- Compare the beads with each other: beads that are all alike, perfectly round and flawless, come from a mould or an industrial lathe.
Never test coral with acid, vinegar or household products: its material reacts, and you would destroy it. No heated needle either, which leaves marks and does not allow any conclusion.
What these tests do not prove, and the question of protection
A red coral may be dyed, a dyed bamboo can be very well made, and a well-moulded resin can deceive the eye. For a valuable piece, a certificate from a recognised gemmological laboratory specifies the species, whether the colour is natural and the treatments.
Coral is a fragile animal. In the Mediterranean, the harvesting of red coral is regulated: the General Fisheries Commission for the Mediterranean (GFCM) prohibits harvesting colonies with a base diameter under 7 mm, and some countries apply higher thresholds. Scientists consider this threshold low given the slow growth of the species. Reef-building corals, black corals and others are listed in Appendix II of CITES, which requires permits for international trade. To our knowledge, Mediterranean red coral has not been listed to date (a proposal to do so was rejected in 2007): check the current status in the official CITES database before any significant purchase.
If origin matters to you, ask for the species, the fishing area and the import documents. Dyed bamboo coral and alternative materials are options that have nothing to do with fishing precious coral. See also our coral page and our commitments.
Frequently asked questions
How can I recognise real coral?
Look under the magnifier: fine, irregular striations are natural. A grain that is too regular, bubbles, colour in the cracks or a white core at the drill hole suggest dye or an imitation. For a valuable piece, ask for a certificate.
Is bamboo coral fake coral?
It is real coral, but of a different type from precious coral. It is naturally white and often dyed red. It is honest when it is sold as dyed bamboo coral.
Can I test coral with vinegar?
No. Coral is calcium carbonate: acids attack and destroy it. This test must be avoided.
Is coral protected?
The harvesting of red coral is regulated in the Mediterranean, and several groups of corals are listed under CITES. To our knowledge, Mediterranean red coral is not listed to date: check the official database.
Why does my coral change colour?
Coral is soft and porous. It can fade with light, sweat and cosmetics. Store it in a safe place and wipe it with a soft cloth.
Also read
The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Recognising real stones.