Japanese Coral

Buying this stone

Where it came from, what its weight band is for, and what to check before any money changes hands.

The deposit

Japanese coral is a trade category, and the origin line on this listing is deliberately left open. Corallium japonicum, traded as Aka, is denser and more tightly grained than Mediterranean coral and reaches a more vivid, slightly bluer red, which is the material the Indian market prices above all other coral. Separating it from the Pacific species it grows alongside is laboratory work on an organic material, and we have not commissioned that report, so the specification above says the origin is subject to testing rather than asserting what we cannot yet show you. One structural detail holds whichever species this proves to be: the branch carries a white core, so a fully saturated cabochon with no white showing has had material cut away to reach that.

This stone

At 19.58 carats this is a single polished cabochon of real presence, and coral is a light material, so it covers considerably more area per carat than any mineral in the catalogue. A twenty carat coral reads as a much larger stone than a twenty carat sapphire would. Cabochon is the right and traditional cut here because coral is opaque and has no optical business being faceted, and a smooth dome is also the shape that shows the evenness of the colour most honestly, with nowhere for a variation to hide behind a facet edge.

Treatment

Untreated. Coral is dyed on an industrial scale, and bleached, and reconstituted from powder and resin into something that looks like a solid branch, so untreated is a meaningful claim rather than a formality. Japanese material is the most worth faking because it commands the highest prices, and pale Pacific coral dyed to an Aka red is a standard commercial product. Nothing has been done to this piece, which is also why its colour is the colour the polyp laid down rather than a uniform tone applied afterwards.

The report

No report is held for this 19.58 cts red coral stone yet, and we would rather say that than name a laboratory that has not seen it. We will submit it to IGI or IIGJ before purchase on request.

Before you pay

• Look along the surface for the fine parallel longitudinal striations natural coral carries. Reconstituted material has none.
• Check any drill hole or fissure for colour pooling more strongly there than on the surface. That is what dye does.
• Keep it away from perfume, vinegar and household cleaners. This is calcium carbonate and acid attacks it directly.

Read next

Moonga, the red coral covers the material itself and what gets sold in its place. How to buy a coloured stone covers pricing, treatment and reports.

Written by Kamal Kishore Agarwal, founder and gemmologist, Gem-A qualified, buying in Johari Bazaar since 2008.