Coral is bright and even in color, with enough luster and firmness except for no damage, dark cracks and scratches. The most important thing is natural primary colors, but there are many dyed goods in the jewelry market. Coral is mainly composed of calcium carbonate, so it is easy to be colored, but many dyed corals only dye the epidermis, and the color is unnatural and uneven locally. The naked eye can see the white inside. The most effective identification method is to dip a cotton swab in some acetone solution and wipe it in an inconspicuous place. If cotton is red or pink, it means it is dyed, and the original color should not change color. Dyed beads may also gradually change color within a few years. Some dyed goods are dyed blue with low-grade light corals, posing as precious African blue corals. If they are wiped with acetone solution, they will show faded blue dye on cotton. When black coral is dyed black, black dye will fall off. The solvent for removing nail polish also contains acetone, which can also be used as a true and false color detector for coral. Other dyed articles are not coral at all, but may be dyed with marble (granular), fish glue, calcined bone, glass (foaming), plastic (light weight), plant buds, rubber and gypsum mixture. None of them have the uneven stripes peculiar to natural corals. If a drop of hydrochloric acid is tested in an inconspicuous place, the fake product will not bubble as quickly as the real one.