Asian & Tribal Art
in Pompano Beach

Jade is a density question, not a color question

Two different minerals are sold as "jade," and a third is often passed off as one. Nephrite is a tremolite-actinolite amphibole: Mohs hardness 6–6.5, specific gravity about 2.95 (reference range roughly 2.90–3.10) and refractive index around 1.61–1.63. Jadeite is a sodium-aluminum pyroxene: hardness 6.5–7, specific gravity near 3.33 (published ranges run about 3.24–3.43) and a spot refractive index near 1.66. Serpentine, including bowenite, which the trade calls "Suzhou jade," is lighter and softer. One GIA lab note recorded a spot RI of 1.56 and an SG of about 2.56 on an antigorite cabochon.

The gap between 2.95 and 3.33 is wide enough for a simple hydrostatic test. Weigh the loose piece in air, weigh it suspended in water, then divide the air weight by the difference between the two. A jadeite bangle should feel noticeably heavy for its size, and a serpentine one noticeably light. A mounted or lacquered piece cannot be weighed this way, and the result shows the material, not the age.

Texture and polish give supporting clues. Polished jadeite is glassy (vitreous) and more granular, while nephrite looks oilier and finer-grained. Color proves nothing, because all three come in green. GIA notes that green omphacite can closely resemble fine jadeite and needs advanced testing to separate. In one instrument paper (Mendoza Cuevas and Fernandez-de-Cossio Dorta-Duque, arXiv:1610.06295), a portable X-ray diffraction and fluorescence unit was trialed on jadeite and omphacite stones, which shows how far the question goes beyond a loupe.

Material also helps with dating. Chinese jade carving is generally described as nephrite until large-scale jadeite imports from Burma arrived in the 18th century, so a jadeite piece sold as a Shang or Han antiquity is a red flag.

Ivory, bone and the federal rules a seller must respect

Elephant ivory has a signature that bone lacks. In cross-section, curved lines cross to form a lattice called the Schreger pattern. Espinoza and Mann (Journal of the American Institute for Conservation, 1993, 32(3):241–248) found that the outer angles are obtuse, above 115°, in modern elephant ivory and acute, below 90°, in woolly mammoth. Readings in between are not a clean call. The pattern also needs a transverse section, so a finished figure may offer only its base or a damaged edge. Bone shows no lattice. Look instead for Haversian canals, which appear as tiny dark pits, dots or streaks. The Western Australian Museum's conservation manual adds that chemical tests usually cannot separate bone from ivory, so a hot pin or a spot test is not a reliable answer.

The U.S. rule on African elephant ivory took effect July 6, 2016. In summary:

• Antique exception: the item must be at least 100 years old and contain a listed species. It must not have been repaired or modified with that material on or after December 28, 1973, and it must have entered through a designated port if imported. The seller must be able to prove the age.
• De minimis exception: the ivory must be a fixed or integral part, under 200 grams in total, and not the primary material of the piece (more than 50 percent of volume counts as primarily ivory). For items in the U.S., the ivory must also have been imported before January 18, 1990.
• Scope: the rule targets African elephant ivory. Asian elephants are also ESA-listed and CITES-protected, and the antique rules apply to them as well.

Florida has no statewide ban on in-state ivory sales, according to a 2023 Humane Society report. That report found suspected ivory in 20 of 46 Florida stores visited, and only two vendors claimed to have the paperwork. The same advocacy group counted 13 states with their own laws. A Broward estate sale might stay in state, but a sale to a buyer in another state brings the federal rules into play.

Reign marks and bronze patina: what the surface really says

A six-character mark such as 大明宣德年製 reads Da Ming Xuande nian zhi: "Great Ming, made in the Xuande years." It is normally set in columns read top to bottom and right to left, in regular script. The mark is a claim made by the maker, and often not the original maker. Kangxi-period blue-and-white frequently carries Ming marks, and Xuande and Chenghua are among the most copied. Some of these were homage rather than fraud. The Asian Art Museum notes that Qing imperial kilns often marked imitations with the reign of the period in which they were actually made. Bronze is no safer: Bruce Rusk's abstract on Xuande-style incense burners says their origins are uncertain, and that books purporting to authenticate them are later forgeries. Judge the body, glaze, foot and form first, and treat the mark as a footnote.

Bronze patina is chemistry you can read. Archaeological bronzes often show red cuprite under a green layer of malachite (copper hydroxy carbonate) or atacamite/paratacamite (copper hydroxychlorides, Cu₂(OH)₃Cl), with blue azurite in places. The danger is bronze disease. Cuprous chloride (nantokite) can sit hidden under sound-looking green, then react with moisture and oxygen to form pale green powdery trihydroxychlorides. The reaction expands the metal and can crack it.

David Scott's review (Journal of the American Institute for Conservation, 1990, 29(2):193–206) recommends storage at 42–46% relative humidity for most bronzes. He warns that above 55% the reactions become very rapid and may not stop when humidity falls again. In his tests, a compressed cuprous chloride tablet burst within a day at 70%. He also cautions that atacamite or paratacamite on the surface does not by itself prove active corrosion. Identifying the minerals reliably takes X-ray diffraction, not the eye. Do not scrub, and keep the piece dry until someone qualified has seen it.