Coral, the skeletal remains of marine polyps, has been valued for centuries in jewelry and décor. Composed primarily of calcium carbonate, this material forms the hardened structure of complex underwater colonies. Due to its popularity and environmental restrictions, the market is frequently saturated with synthetic and imitation materials. These substitutes, ranging from colored plastics to reconstituted powders, are often passed off as genuine. Understanding the specific physical and visual characteristics of real coral is necessary to confidently identify an authentic piece.
Visual Clues: Surface Texture and Growth Structure
The most reliable method for identification involves observing the structure of the coral under magnification, as its organic origin leaves distinct, non-replicable patterns. Real coral possesses a surface texture that is rarely flawless or perfectly smooth. When viewed closely, this texture often reveals fine, parallel striations or a subtle, granular appearance, sometimes described as resembling wood grain or a fingerprint.
This unique structure is a result of the coral polyp’s skeleton formation, which includes elements like corallites and a sponge-like matrix called coenosteum. The resulting texture may show minute pits or pores, which are remnants of the original organic growth. Imitations made of glass or hard plastic typically present a surface that is unnaturally smooth or displays molded imperfections rather than organic grain.
Color consistency also offers a strong visual clue. Natural coral color is rarely uniform, often exhibiting subtle shading variations, lighter centers, or small patches of color inconsistency. This variation is due to the natural distribution of organic pigments within the skeleton.
Artificially dyed fakes often show overly vibrant or unnaturally uniform coloration. A close inspection of drill holes, crevices, or points where the coral meets a metal setting may reveal a concentration or pooling of dye. This pooling indicates a lighter base color where the artificial coloring did not fully penetrate. The surface sheen of genuine coral is also distinctive, presenting a dull, matte finish when raw and a waxy, slightly greasy luster after being polished.
Tactile and Simple Physical Tests
Physical properties like thermal conductivity and density provide additional testing means. Authentic coral, a calcium carbonate mineral skeleton, is a relatively poor heat conductor. When held, it feels cool to the touch, similar to natural stone, and warms up very slowly in the hand.
Plastic or resin imitations have a much higher thermal conductivity than coral. These fakes warm up much more quickly when held, losing that initial, characteristic coolness. Real coral is denser than most lightweight plastic substitutes, providing an appropriate heft for its size. If a piece feels too light for its volume, it may be plastic, while an overly heavy piece could suggest a glass imitation.
A very small, inconspicuous area can be tested with acetone, commonly found in nail polish remover. Since many fakes are made of white coral or other materials that are artificially dyed, color transfer onto a cotton swab suggests the presence of surface dye rather than natural pigmentation. Highly destructive tests, such as touching the piece with a hot needle to see if it melts, should be avoided entirely on finished jewelry.
A simple, minimally destructive test involves rubbing the piece against an unglazed ceramic tile. Genuine coral is relatively soft, registering between 3 and 4 on the Mohs hardness scale. If performed on a scrap piece, real coral may leave a reddish streak on the tile, while glass or plastic imitations will not.
Recognizing Common Imitation Materials
Identifying the specific material used to create the imitation reinforces the observations made during visual and tactile inspections.
Plastic and Resin
One of the most common substitutes is colored plastic or resin, which can often be detected by its light weight and the presence of faint mold lines or seams. These materials lack the fibrous, organic structure found in the natural coral skeleton.
Glass
Glass is another frequent imitation, often used to simulate the smooth, polished appearance of precious red coral. Glass pieces feel significantly heavier than real coral of the same size and may display an unnaturally high, glossy sheen. A distinct identifier for glass is the potential presence of tiny, spherical air bubbles trapped within the material, which are never found in naturally formed coral.
Dyed Shell or Bone
Dyed shell or bone is frequently used to imitate more expensive varieties of coral. This includes bamboo coral, which is naturally white and subsequently dyed red or pink. These imitations may show a different surface structure under magnification, such as the distinct lamellar or layered pattern of shell, instead of the porous, wood-grain look of true coral.
Reconstituted or Composite Coral
A more sophisticated fake is reconstituted or composite coral, manufactured by mixing pulverized coral powder with plastic resin or cement and then pressing the mixture into a mold. These composite pieces often appear too perfectly uniform and lack the natural, irregular growth patterns characteristic of solid, natural coral.