Black Coral
Black coral is an organic jewelry material composed of scleroprotein, also known as Akaban (a term used in Southeast Asia), Horn Coral, or in Japan, Umi-matsu (sea pine). It was discovered off the coast of Maui, Hawaii in 1958, and is said to have also been confirmed off the coast of New Zealand, Australia, in 1966. In Japan, it has long been known as "fukami-matsu" (deep-sea pine) caught in fishermen's nets and has been used for ornaments in tokonoma alcoves and household altars. Belonging to the Hexacorallia subclass, its skeletal axis is organic rather than calcite; while resistant to acids, it is prone to cracking and deformation due to drying and dehydration.
A material valued for its black texture and characteristic golden-brown stripes and mesh patterns.
Basic Information
| English Name | Black Coral |
|---|---|
| Japanese Name | Kurosango |
| Chemical Composition | Scleroprotein |
| Structure | Amorphous |
| Hardness | 4 |
| Specific Gravity | Approx. 1.3 |
| Classification | Organic gemstone (Coral) |
Characteristics & Varieties
- Other names: Akaban, Horn Coral, and in Japan, Umi-matsu (sea pine).
- Appearance (original): In species like Antipathes japonica, the surface of the trunk is densely covered in fine thorns, and fine golden-brown mesh patterns can be seen.
- Durability: Because the skeleton is organic, it is resistant to acid but is prone to cracking and deformation due to drying and dehydration.
Varieties
- White-patterned coral: Formed when concentric gaps appear in the trunk or branches, where lime deposits to create white arc-shaped stripes. However, some white patterns are created via filling treatments.
Origin, Synonyms, Treatments, & Simulants
Treatments (Important Cautions):
- Bleaching: Some items are bleached with hydrogen peroxide (H2O2) to resemble golden coral. Because this makes the material brittle, it is sometimes reinforced with synthetic resin, in which case air bubbles may be visible under a loupe.
- Black resin coating: Many black coral products currently on the market are coated in black resin, which may obscure the original "golden-brown" stripes or mesh patterns. If the coating is thick, it is difficult to inspect the interior, making it necessary to be wary of items with unknown composition.
Trade Names:
- Coral Jet: A completely fabricated name.
Simulants:
- Sea Fans: A type of octocoral whose skeleton is blackish and whose tree-like shape is somewhat similar.
- Tortoiseshell: Processed "black shell" is often mistaken for black coral due to its light specific gravity (see the page on tortoiseshell).
Caution: Black coral is frequently subjected to "appearance-altering treatments" such as black coating, bleaching, or resin infusion, making it difficult to judge the true nature and condition of the material by appearance alone. In particular, items with thick black coatings that obscure the interior or have unknown contents carry high risks. When purchasing, ensure thorough inspection with a loupe and verify the consistency of product descriptions. Additionally, as the material is prone to cracking and deformation due to drying, it is safest to store and handle it in an environment that is not overly dry.