su01

pg. 149

EDITORIAL

REGULAR FEATURES

pg. 115

96

FEATURE ARTICLES

Based on recent visits to the pearl farms of Hanzhou Province, the authorsreport on the latest techniques being used to produce Chinese freshwatercultured pearls.

Shigeru Akamatsu, Li Tajima Zansheng, Thomas M. Moses, and Kenneth ScarrattThe Current Status of Chinese Freshwater Cultured Pearls

95Alice S. KellerThe G&G Twenty Year Index: Two Decades of Evolution

124

A new polishing process is being used to create the appearance of aster-ism in gems that have seldom if ever shown this phenomenon previously.

Shane F. McClure and John I. KoivulaA New Method for Imitating Asterism

114

UV-Vis reflectance spectra and fluorescence characteristics are useful indistinguishing undrilled natural- and treated-color yellow cultured pearlsproduced from the Pinctada maxima mollusk.

Shane Elen

Spectral Reflectance and Fluorescence Characteristics of Natural-Color and Heat-Treated Golden South Sea Cultured Pearls

130 Banded twinned diamond crystal Diamonds with unusual inclu-sions Feldspar with chrome diopside inclusions Gibbsite dyed to imitate nephrite Devitrified glass resembling jade Early Japaneseassembled cultured blister pearls Dyed black faceted cultured pearls New imitation: Shell pearls with a calcite bead

Gem Trade Lab Notes

163 Gemological Abstracts171 Guidelines for Authors

160 Book Reviews

137 Thank You, Donors138

Royal Asscher cut Canadian diamonds PDAC conference A diamondtable with trigons Burmite Cats-eye amethyst Brownish red to orange gems from Afghanistan/Pakistan Clinohumite from Tanzania An engraved emerald Unusual rutilated quartz Rubies and ruby deposits of eastern Madagascar Ruby crystal with a mobile bubble Green sapphire with pyrochlore inclusions Vortex (Yogo Gulch) sap-phire mine update Canary tourmaline from Malawi Bismuth-bearingliddicoatite from Nigeria Jurassic Bugs amber imitation Assembled diamond imitations from Brazil Enamel-backed quartz as a star sapphireimitation Goldschmidt conference Moscow gemological conference Harvard tourmaline exhibit

Gem News International

pg. 108

pg. 133

VOLUME 37, NO. 2Summer 2001

NOTES AND NEW TECHNIQUES

t has been just over 20 years since Gems & Gemologywas redesigned and the new format introduced.

Looking at the dozens of covers of these issues, whichdominate the walls of my office, I think of the incredibleeffort that went into each onethe thousands of hoursthat our authors and staff invested in every issue to dothe research, write and refine the articles, and acquire thebest illustrations. I also think of Harold and Erica VanPelt, who photographed the vast majority of the coverimages, as well as the many individuals who loaned valu-able gemstones and jewelry for them to capture on film.

What am I proudest of? The quality of the informationand the depth of knowledge each issuerepresents. Today, 20 years after thefirst issue of the redesigned G&Gappeared, the articles in that issueonperidot from Zabargad, cubic zirconia,and the detection of diamond simu-lantsare just as solid and useful asthey were in April 1981. Certainly,since then there have been new peridotlocalities, changes in CZ, and morediamond simulants, but these articlescontinue to serve as a solid base forongoing research on those topics.

In the past two decades, we havepublished over 5,500 pages of timelyand timelessarticles, Lab Notes,Gem News entries, Book Reviews, andGemological Abstracts. This is truly a treasure chest ofinformation. But how do you access it? How do you findwhat you need?

We are pleased to provide a solution: our TwentyYear Index (19812000). We have revised and updatedthe subject and author listings from our first 15 years,and added the annual indexes for the last five.

In the course of preparing this Index, we were allstruck by the changes that were necessary since ourfirst index was published in Winter 1981changes notonly in gemology, but also in geography and technolo-gy, many of them interrelated.

For example, the most significant change to the geopo-litical landscape since the Spring 1981 issue has been thebreakup of the Soviet Union. For our industry, however,this change has been more profound than the simplereplacement of names on a map. With the new socioeco-nomic climate in this region has come an influx of natu-ral gem materials onto the world marketmost notablyfrom the release of diamonds that were in the governmentstockpile, but also from renewed mining activity for suchclassic gems as demantoid garnets. There also has been anunprecedented impact on the availability of syntheticgem materialsnew synthetic rubies, sapphires, emer-alds, and quartz varieties, to name but a few. Russian high

pressure/high temperature (HPHT) presses are now syn-thesizing diamonds in virtually every color.

In other regions, names that were unknown to most ofus only five years ago are now part of the gemological par-lanceTunduru in Tanzania, Ilakaka in Madagascar,Ekati in Canada. The availability of these significant newdeposits of sapphires, rubies, and diamonds has shiftedthe balance of supply and demand. At the same time, ithas presented greater challenges to gemologists in identi-fying sources and treatments.

Scientific advances in the U.S. and elsewhere alsohave brought us synthetic moissanite, the first diamond

simulant to match the thermal proper-ties of diamond. Whereas there wasalmost nothing written on diamondtreatments in the 1980s, articles ondiamonds that have been fracturefilled or HPHT processed are promi-nent in the current index. Our firstindex simply referred to spec-troscopy. Today, there are entries formore than 10 different types of spec-troscopy. Laser Raman microspec-trometrywhich we first reported ononly three years agois now used rou-tinely in major gem labs around theworld to identify inclusions and gemmaterials, as well as to recognizeHPHT annealing in diamonds.

For this veteran of two decades of G&G, the AuthorIndex offered a distinct pleasure as I was reminded ofthose who have contributed so much to the journal.Godfathers of gemological research such as RobertCrowningshield, Edward Gbelin, Richard T. Liddicoat,and Kurt Nassau were joined by an impressive group ofnew researchers such as Emmanuel Fritsch, Henry Hnni,Bob Kammerling, Bob Kane, John Koivula, ShaneMcClure, Tom Moses, Ken Scarratt, Karl Schmetzer, andJames Shigley, among many others.

We hope that you too will enjoy using the index andfind it a valuable reference tool. Explore the thousandsof entries to learn what you need to know to stayabreast of the rapidly evolving world of gemology.

Alice S. KellerEditor

[email protected]

Note: See the ad on page 159 of this issue to purchase a printedcopy of the Gems & Gemology Twenty Year Index, or access itfree of charge by visiting us online at www.gia.edu/gandg.

EDITORIAL GEMS & GEMOLOGY SUMMER 2001 95

The GG&&GG TTwweennttyy YYeeaarr IInnddeexx:

Two Decades of Evolution

I

THE CURRENT STATUS OF CHINESEFRESHWATER CULTURED PEARLS

96 CHINESE FRESHWATER CULTURED PEARLS GEMS & GEMOLOGY SUMMER 2001

demand for information, two of the authors (SAand LTZ) visited six FWCP farms and one nucleusmanufacturer in Chinas Zhejiang district; theyalso examined hundreds of Chinese FWCPs. Thetrip was made from July 25 to 29, 2000; informa-tion in this article has been confirmed and updat-ed since then based on the second authorsmonthly trips to the pearl-farming areas to visithis pearl factory in Zhuji City, as well as to pur-chase freshwater cultured pearls for export. Inaddition, the first author has visited Chinesefreshwater pearl-culturing areas several times dur-ing the past two years. This article reports on thecurrent status of the Chinese freshwater culturedpearl, both the various culturing techniques usedand the cultured pearls themselves, updating (andsuperseding) the pearl-culturing information inScarratt et al. (2000).

By Shigeru Akamatsu, Li Tajima Zansheng,Thomas M. Moses, and Kenneth Scarratt

See end of article for About the Authors information and Acknowledgments.GEMS & GEMOLOGY, Vol. 37, No. 2, pp. 96113 2001 Gemological Institute of America

Chinese freshwater cultured pearls (FWCPs) are assuming a growing role at major gem and jewelry fairs, andin the market at large. Yet, it is difficult to obtain hard information on such topics as quantities produced, inwhat qualities, and the culturing techniques used because pearl culturing in China covers such a broad area,with thousands of individual farms, and a variety of culturing techniques are used. This article reports onrecent visits by two of the authors (SA and LTZ) to Chinese pearl farms in Hanzhou Province to investigatethe latest pearl-culturing techniques being used there, both in tissue nucleation and, much less commonly,bead (typically shell but also wax) nucleation. With improved techniques, using younger Hyriopsis Cumingimussels, pearl culturers are producing freshwater cultured pearls in a variety of attractive colors that are larg-er, rounder, and with better luster. Tissue-nucleated FWCPs can be separated from natural and bead-nucle-ated cultured pearls with X-radiography.

he popularity of Chinese freshwater cul-tured pearls (FWCPs) has risen dramaticallyin the worlds markets. The unique charac-

teristics of the Chinese FWCPin terms of size,shape, and colorhave been key to this popularity(figure 1). Chinese FWCPs are available in sizesranging from 2 mm to over 10 mm; in an interest-ing variety of shapes such as round, oval, drop,button, and baroque; and in rich colors such asorange and purple, often with a metallic luster.The vast majority of these Chinese FWCPs arenucleated by mantle tissue only, although somenucleation with spherical beads has taken place(Bosshart et al., 1993; China producing nucleatedrounds, 1995; Matlins, 1999; China starts...,2000; Scarratt et al., 2000). This makes them dis-tinct from the overwhelming majority of culturedpearls from other localities, which are bead nucle-ated. Despite the growing popularity of ChineseFWCPs, details concerning their history, culturingareas, production figures, culturing techniques,and the characteristics of the pearls themselvesare not widely known. In response to the growing

T

CHINESE FRESHWATER CULTURED PEARLS GEMS & GEMOLOGY SUMMER 2001 97

HISTORYThe culturing of freshwater pearls was widespreadin China by the 13th century. Tiny figures ofBuddha formed of lead were cemented onto thenacreous interior of the shell produced by the fresh-water mussel Cristaria plicata (zhou wen guanbang in Chinese). Over time, the mollusk coatedthe lead figures with nacre, and the blister pearlsthus cultured were used as temple decorations oramulets (Ward, 1985; Webster, 1994). Even now,this culturing technique survives, although theimages are larger and nucleated with wax ratherthan lead (figure 2). Today, images of Buddha, flow-ers, birds, animals, and other forms are molded withwax and inserted into the mussels. A similar tech-nique is used to create the mab-type hemisphericcomposite cultured blister pearls in white- andblack-lipped pearl oysters, as well as in abalone(Wentzell, 1998).

Freshwater pearl culturing was attempted inJapan around 1910, but success was not achieveduntil 1924, when growers changed from theKarasu mussel (C. plicata) to the Ikecho mus-sel (Hyriopsis schlegeli). Following this success,commercial freshwater pearl culturing began inJapan in 1928. A bead-nucleating technique wasfirst adopted, but growers eventually recognizedthat tissue nucleation produced better results. In1946, freshwater-pearl farmers switched to tissue

nucleation, creating unique freshwater culturedpearls. Since then, Japanese FWCPs have beenhighly prized as Biwas (named after Lake Biwa,

Figure 2. The culturing of freshwater blister pearls waswidespread in China by the 13th century. Tiny figuresof Buddha were cemented onto the inner shell offreshwater mussels (Cristaria plicata), where theywere coated with nacre. The same culturing techniquesurvives today. Instead of tiny lead figures, larger waximages are commonly used to produce a variety offorms, although Buddha (as seen in this 8.3 10.8 cmshell) is still popular. Photo by Shigeru Akamatsu.

Figure 1. Chinese fresh-water cultured pearlsoccur in a variety ofattractive shapes andcolors, as well as in sizesover 10 mm. The potato-shaped Chinese FWCPsin the strand on the leftrange from 9.3 11.3mm to 10.6 12.7 mm.The near-round ChineseFWCPs on the right areapproximately 910mm. Photo Harold &Erica Van Pelt.

where most were grown). Over time, improve-ments in the culturing technique produced morepearls of better quality, and the Japanese freshwa-ter pearl culturing industry flourished. Pearl cul-turing at Lake Kasumigaura began in 1962, and in1980 production reached a peak of 6.3 tons.Production began to decline because of water con-tamination and the high mortality of the mussels(Toyama, 1991). By 1998, production of Japanesefreshwater cultured pearls had dropped to 214 kg,only 3.4% of the peak in 1980 (Statistics of fish-ery and cultivation, 2000).

It was in the late 1960s and early 1970s thatChina started full-scale FWCP production, and low-quality irregular-shaped cultured pearls with wrin-kles on their surface (commonly known as RiceKrispie pearls) appeared in the market (Hiratsuka,1985; figure 3). According to trade statistics pub-lished by the Japanese Ministry of Finance, in 1971Japan imported only 600 grams of this material.Over the next 13 years, however, these importsincreased dramatically: They reached 7.5 tons in1978, 34 tons in 1983, and over 49 tons in 1984.Most were not consumed by the Japanese market,but instead were exported to Germany,Switzerland, Hong Kong, the Middle East, and theU.S. by Japanese distributors (Chinese FWCPsaccounted for more than half the pearls exportedfrom Japan in 1984). In the late 1980s, however, thedemand for such low-quality pearls quickly dieddown, and the Chinese FWCP almost disappearedfrom the world market.

In the 1990s, however, Chinese FWCPs reap-peared, with their quality remarkably improved(China starts pearling revolution, 2000).Culturers had changed the species of mussel fromC. plicata to Hyriopsis cumingi, which is general-ly called the triangle mussel (san jiao or sanjiao bang in Chinese) because of its shape (figure4; Fukushima, 1991). The triangle mussel inhabitswide areas along the Chang Jiang (Yangtze) River.Using the new mussel, growers started to culti-vate 34 mm pearls with a smooth surface.Although some of these Chinese FWCPs werenear-round, more often the commercial producthad a bulbous oval potato shape (again, see fig-ure 1). Over the last decade, quality continued toimprove. Chinese cultivators now produceFWCPs in sizes from 2 mm to over 10 mm, inshapes from extreme baroque to perfect round,and in colors from white to pastel orange and pur-ple, often with a metallic luster.


Figure 4. Chinese pearl farmers greatly improved the qualityof their product in the 1990s by changing the mussel speciesfrom Cristaria plicata to H. Cumingi, the Chinese triangle

mussel. With the use of H. Cumingi both as donor of the man-tle tissue and for culturing, they produced larger culturedpearls with a smoother surface, rounder shape, and better

color and luster. In particular, the color and luster of themother-of-pearl in the tissue-donor mussel has a strong influ-ence on the color and luster of the final cultured pearl; notice

the differences among these four mussels, all of which wereused to provide mantle tissue nuclei. Although earlier cultur-ing with H. Cumingi was done using 22.5 year old mussels,these one-year old mussels are typical of the age at which H.Cumingi are nucleated today. Photo by Shigeru Akamatsu.

Figure 3. Most of the Chinese FWCPs cultivated withCristaria plicata were of low quality: irregular shaped

with many wrinkles on their surface (hence called RiceKrispies; here, 5 8 mm to 9 14 mm, produced in

1976). These pearls first appeared on the market in thelate 1960s and early 1970s, with 600 grams imported

into Japan in 1971. The quantity increased dramaticallyover the next several years (with Japanese imports of 49

tons in 1984), but the boom had faded by the late 1980s.Photo by Maha Tannous.

CULTURING AREAS ANDPRODUCTION AMOUNTThe culturing region for Chinese FWCPs extends overwide areas along the Chang Jiang (also known as theYangtze) River (figure 5). The provinces of Jiangsu,Zhejiang, Anhui, Fujian, Hunan, and Jiangxi are themain culturing areas, with Jiangsu and Zhejiangaccounting for nearly 70% of the total FWCP produc-tion (He Xiao Fa, pers. comm., August 2000).

It is generally thought that pearls cultured insouthern farms grow faster, coinciding with therapid growth of the mussel. By contrast, pearls cul-tured in northern farms grow more slowly, but theircompact nacre gives them a better luster. For thisreason, some farmers who own both northern andsouthern farms initially cultivate pearls in thesouthern farms to accelerate nacre growth, thenmove the mussels to northern farms one year beforeharvest to improve the luster. In addition, northernfarmers often buy nucleated mussels from southerncultivators. According to several pearl culturers inthe cities of Zhuji and Shaoxing, transferring mus-sels from one farm to another during the pearlgrowth period (which may take up to six years) isnot uncommon in China.

No accurate production figures exist for ChineseFWCPs. Two major culturers, He Xiao Fa ofShanxiahu Pearl Co. Ltd. and Ruan Tiejun of FuyuanPearl Jewelry Co. Ltd., estimate that annual produc-tion is currently about 1,000 tons. Because there areseveral thousand pearl farms, many of which arevery small, it is impossible to give an accuratecount. The farms range from major operations withover one million mussels, to tiny roadside swampsdiverted from rice paddy fields that contain tens ofthousands of mussels (see, e.g., figure 6). The mus-sels are suspended in nets (each typically containingtwo to three mussels; figure 7) from buoys that areoften made of Styrofoam or recycled plastic bottles.

RECENT DEVELOPMENTS INTISSUE NUCLEATIONFrom observations made during our frequent visits,and from conversations with several leading pearlfarmers, we confirmed that the vast majority of fresh-water cultured pearls produced in China today are, asstated in Scarratt et al. (2000), mantle-tissue nucleat-ed. As the recent improvement in quality demon-strates, the growth techniques used to create theChinese product have changed. Some of the changescan be counted as major technical improvements.

New Mussel Species Used for Culturing. As notedabove and in Scarratt et al. (2000), Chinese pearlcultivators have changed from the C. plicata mus-sel to the H. cumingi (triangle) mussel. H.cumingi is a large bivalve of the same genus as theH. schlegeli used for pearl cultivation in JapansLake Biwa. Triangle mussels can produce attrac-tive FWCPs with a smooth surface. With the intro-duction of hatchery techniques to propagate the H.Cumingi, mass production of mussels has becomepossible and enormous amounts are now used forpearl culturing.


Figure 5. Freshwater pearl culturing areas extendwidely along the Chang Jiang (Yangtze) River,including the provinces of Jiangsu, Zhejiang, Anhui,Fujian, Hunan, and Jiangxi. Mussels that have beentissue nucleated are not always cultivated in a singlefarm for the entire culturing process. Often they aretransferred to other farms in different provinces,where cultivation continues.

A Longer Culturing Period. In the past, it was com-mon for growers to perform tissue nucleation ontwo-and-a-half-year-old mussels, cultivate them fortwo to three years thereafter, and harvest 47 mmpearls (see, e.g., Jobbins and Scarratt, 1990). In recentyears, however, some growers have been operatingon significantly younger mussels, approximatelyone to one-and-a-half years old (figure 8, right), andcultivating them for four to six years. By extendingthe period between insertion of the tissue nucleiand the harvest, they have succeeded in producingcommercial quantities of FWCPs larger than 8 mm.A one-year-old mussel has a small shell, one valveof which weighs only 10 grams (average dimen-sions: 7.2 4.3 cm) at the time of nucleation. Thatsame valve will attain a shell weight at harvest after

five years of 260 grams (up to 16.4 10.5 cm), morethan 25 times its starting weight (figure 8, left). Thepearls grow as the mussels grow, but the rate ofgrowth is not always proportional.

Even though the cultivation period from nucle-ation to harvest is the same for any given mussel,the growth rate of the many pearls nucleated in thatmussel is not the same. Consequently, FWCPs ofvarious sizes are harvested from a single mussel (fig-ure 9). Table 1 lists the different sizes of FWCPsremoved from a sample harvest of four mussels thatwere cultivated for 4.5 years in a farm in Shaoxing.


Figure 6. In China, the number of farms culturing freshwater pearls is too large to be counted accurately. Theyvary in size from large lakes (left) to small farms converted from rice paddy fields (right). Note the soil piledaround the paddy field to keep the water deep enough (1.5 m) for pearl culturing. Photos by Shigeru Akamatsu(left) and Li Tajima Zansheng (right).

Figure 7. During pearl cultivation, two to threemussels typically are put in a net and suspended inthe water from Styrofoam buoys or recycled plasticbottles. Photo by Shigeru Akamatsu.

Figure 8. A one-year-old triangle mussel at thetime of tissue nucleation is very small (right)anaverage of 7.2 4.3 cm, with an approximate shellweight (one valve) of 10 grams. A six-year-old H.cumingi mussel at the time of harvest (left) afterfive years of cultivation is very largeup to 16.4 10.5 cm, with a single valve now 260 grams inweight. Photo by Li Tajima Zansheng.

These results also indicate that cultivation periodsof 4.5 years can produce FWCP sizes of over 9 mm.Note that these mussels were older and larger whenthe nuclei were inserted than is currently practiced

Improvement in the Mantle Tissue Nucleus. In ear-lier freshwater pearl culturing, a common techniquewas to cut a 2 2 mm piece of tissue from the man-tle of a 2.5-year-old mussel, fold it, and then insert itinto a pocket made in the mantle lobe of a host mus-sel (Jobbins and Scarratt, 1990). Because this piece oftissue was too thick to be worked into a roundshape, most of the FWCPs produced had shapes suchas rice, oval, and baroque. Recently, pearl farmershave changed the nature of the mantle-tissue nuclei.Instead of taking the tissue from a 2.5-year-old mus-sel, growers now use a one-year-old (H. cumingi)mussel for this part of the procedure. When a pieceof tissue is removed from such a young mussel, it isthin enough to be rolled into a round ball. So the cul-turer now cuts a larger (but thinner) 4 4 mm pieceof mantle tissue (figure 10), and makes it as round aspossible by rolling it before nucleation (figure 11).

Improvements in the Nucleation Technique. Fromtheir experience, pearl culturers identified that theposterior mantle lobe of the mussel, where the moth-er-of-pearl has the desired color and luster, is the keylocation to produce a better-quality pearl with finecolor and luster (again, see figure 4). So they started tocut pieces of tissue from the posterior part of the sac-rificed donor mussel and then placed them intopockets in the same posterior mantle lobes of thehost mussel (figure 12). With this new technique,

pearl culturers are improving the color and luster oftheir FWCPs. Figure 13, taken in April 2001, shows agroup of technicians performing different stages ofthe pearl nucleation technique at this pearl-process-ing operation in a suburb of Zhuji City.

Another improvement is the reduction in thenumber of tissue pieces used to nucleate a singlemussel. In the past, when cultivators used relative-ly large, 2.5-year-old mussels to begin the process,about 20 pieces usually were inserted in each man-tle lobe of the bivalvefor a total of about 40pieces in a single mussel (Farn, 1986; Scarratt etal., 2000). Now, some growers typically insert 14or fewer pieces of tissue in each mantle lobe of aone-year-old musselfor a total of 28 or fewer ineach mussel (figure 14).


Figure 9. All the Chinese FWCPs in this photo weretissue nucleated and harvested from both valves ofone mussel after 4.5 years. Even though the culturingconditions were the same, the resulting FWCPsrange from 5 to 9 mm. Photo by Shigeru Akamatsu.

TABLE 1. Freshwater cultured pearls produced from four mussels harvested inShaoxing after cultivation for 4.5 years.a

Mussel 1 Mussel 2 Mussel 3 Mussel 4

Size (mm) No. of % of No. of % of No. of % of No. of % of FWCPs total FWCPs total FWCPs total FWCPs total

4 0 0 1 2.9 2 3.8 0 05 4 9.5 5 14.3 20 37.7 1 3.06 12 28.6 13 37.1 21 39.6 8 24.27 13 31.0 12 34.3 6 11.3 16 48.58 10 23.8 3 8.6 3 5.7 8 24.29 3 7.1 1 2.9 1 1.9 0 0

Total 42 35 53 33

aNote that these mussels were older when they were nucleated, and had more nuclei inserted, than pearl farmersnow prefer.

Movement of Mussels Among Different Farms. Weobserved not only that culturers sold the live, oper-ated mussels for further growth in the farm ofanother producer, but also that as they recognizeddeficiencies or changes in the environments oftheir farms, they often moved their own mussels tomore suitable farms. Culturers also have found thatthe change in farms places the mussels under atype of stress that activates their respiration sothat they produce more carbon dioxide (Koji Wada,pers. comm., 2001). The carbon dioxide converts tocarbonate ions that combine with the calcium ionsto form more calcium carbonate crystals. Thisimproves the nacre growth, thus promoting goodluster and color, as well as larger pearls.

FWCP CULTIVATION WITH SOLID NUCLEIAlthough, as noted above, the vast majority ofChinese FWCPs currently are tissue nucleated, vari-ous methods to culture the FWCP by inserting asolid bead nucleus are being practiced (China pro-ducing nucleated rounds, 1995). Use of a beadnucleus is still being done on a limited scale only,because of the higher cost of production and theinferior quality of the pearls produced. According to


Figure 12. The operator places a one-year-old musselon a fixing stand and opens the shell with care, mak-ing pockets in the posterior mantle lobes and insertingrolled pieces of mantle into them, as illustrated in thediagram (inset). A skilled technician can operate on120 mussels a day. Photo by Shigeru Akamatsu.

Figure 10. Using a knife, the technician cuts apiece approximately 4 4 mm from a strip of tissuethat was removed from the mantle lobe of an H.Cumingi mussel of about the same age as the one-year-old H. Cumingi into which it will be inserted.Photo by Shigeru Akamatsu.

Figure 11. Just before nucleation, the thin pieces ofmantle tissue are rolled as round as possible.Because the piece of mantle tissue is so thin, it canbe rolled into a round ball more efficiently than thethicker (2 2 mm) pieces of tissue that were typi-cally used in the past. Photo by Shigeru Akamatsu.

Chinese pearl-culturing textbooks (Li and Zhang,1997; Li, 1997), the main methods used to beadnucleate Chinese FWCPs are as described below.

Insertion of Bead Nuclei into Mantle Pockets. TheChinese textbooks cited above report that pocketsare cut into the mantle lobes of large and healthyfive- to eight-year-old H. cumingi mussels, and thesame round shell beads typically used for saltwaterpearl culturing are inserted together with pieces oftissue cut from the mantle of another H. Cumingimussel (figure 15). The implantations typicallytake place from March through May and fromSeptember through November, but the latter periodyields better results.

The spherical bead nucleus varies from less than2 mm to over 8 mm, while the piece of mantle tis-sue usually is smaller than 2 2 mm. For the bestproduct, the size of the piece of tissue must be con-sistent with the size of the bead nucleus. When thepiece of tissue is too large relative to the bead,pearls with a poor shape, wrinkles, or blemishescommonly result. Conversely, according to thetextbooks, if the piece of tissue is too small, it caneasily separate from the nucleus, resulting in a tis-sue-nucleated FWCP and the possible expulsion ofthe bead. The solid nucleus normally is cut fromthe interior of a Chinese or American freshwater

mussel (see The Bead Nucleus section below),but paraffin wax also is used by some pearl farmers.

When paraffin is used, typically spherical waxbeads about 2 mm in diameter are inserted into amussel (H. cumingi) to produce 57 mm FWCPs (fig-ure 16). If these cultured pearls are heated whendrilled, the liquefied paraffin will ooze out of thedrill hole, leaving a small hollow core. Solvents suchas bleaching reagents can easily enter such hollowFWCPs, facilitating this processing. Thus, the use ofparaffin nuclei has a possible three-fold purpose: (1)produce round pearls, (2) lower the cost of the nucle-us, and (3) facilitate processing after harvest.

Modified Direct (or D) Operation. This method issimilar to that used in South Sea and Tahitian pearlcultivation, with the exception that (as noted above)


Figure 13. Several technicians are simultaneouslypreparing the mantle tissue and inserting thepieces into the young H. Cumingi mussels at thispearl-processing operation in a suburb of ZhujiCity. Photo by Li Tajima Zansheng. Figure 14. Shown here is a one-year-old mussel just

after a tissue-nucleating operation in July 2000. Inaccordance with the current practice of this cultivator,14 pieces of mantle tissue were inserted into the poste-rior part of each of the two mantle lobes (to produce atotal of 28 pearls). In recent years, fewer pieces ofmantle tissue have been used to facilitate the produc-tion of larger FWCPs. Photo by Shigeru Akamatsu.

the bead nuclei are inserted into the mantle of thehost mussel for (freshwater) Chinese cultured pearls,whereas for (saltwater) South Sea and Tahitian cul-tured pearls the bead is inserted into the gonad. Aftera mussel nucleated by the usual tissue-insertionoperation is harvested, the technicians carefully cutout the FWCPs and then, rather than discarding theanimal, they insert a shell bead nucleus into eachpearl sac where a tissue-nucleated FWCP had grown(figure 17). With this procedure, there is no need toinsert a piece of tissue with the bead nucleus becausethe pearl sac is already formed. Usually bead nuclei56 mm in diameter are inserted into pearl sacsformed in the mantle lobes, and culturing continuesfor one to two years. Because at the time of the firstharvest the mussel is already a little old, the colorand luster of the bead-nucleated pearl produced bythis second procedure typically will not be as good asthat of the original tissue-nucleated FWCP (Li andZhang, 1997; Li, 1997). Nevertheless, some attractivepearls have been cultured by this process (figure 18).


Figure 16. Recently, small paraffin balls also havebeen used as bead nuclei. When the cultured pearlis heated during drilling, the wax can melt out,leaving a small void that makes treatment easier.The cultured pearls shown here are 57 mm indiameter. Photo by Maha Tannous.

Cut a tip of mantle lobe

Make a pocket with a needle

Insert a nucleus into the pocket

Push the nucleusinto proper positionin the pocket

Place a small piece of mantle tissue into the pocket with the nucleus

Operation finished

1

2

3

4

5

6

BEAD NUCLEUS INSERTIONBEAD NUCLEUS INSERTION

Figure 15. Bead nucleation of Chinese FWCPs usuallyinvolves insertion of the bead nucleus together with apiece of mantle tissue into a pocket made in the man-tle lobe. Most commonly the beads are fashioned fromthe shell of a Chinese or American freshwater mussel.Adapted from Li (1997).

Insertion of the Bead into the Mussels Body. Tomake FWCPs over 10 mm, relatively large nuclei (8to 12 mm in diameter) are inserted together withpieces of tissue into the body of the H. cumingi mus-selas distinct from the mantle lobes in the bead-nucleation procedure described earlierusuallyunder the liver and/or the heart (figure 19). This is thesame technique currently used to produce Kasumigafreshwater cultured pearls in Japan (Hnni, 2000).

The Bead Nucleus. Japan was once the only countrythat manufactured shell bead nuclei for pearl cultur-ing, but now China also produces and supplies shellbeads to Chinese pearl culturers. By visiting one ofthe nucleus manufacturersTheng Xuan An ofPenfei Youhezenzhu Co., Zhujitwo of the authors(SA and LTZ) learned about some of the Chinesenuclei. In China today, bead nuclei for saltwater aswell as freshwater pearl culturing are fashioned


Figure 18. These Chinese FWCPs were bead nucle-ated by a modified D operation. The cross-sec-tion is 8 mm in diameter; the whole samples rangefrom 7.5 mm in diameter to 9 10 mm. Photo byMaha Tannous.

Place a curved holder on the inner surface of the mantle next to the pearl sac

Cut open the tip of the pearl sac with a bladed needle

Remove the cultured pearl from the pearl sac by pushing with the curved holder

Insert a bead nucleus into the new vacant pearl sac and continue cultivation;there is no need for a piece of mantle to accompany the bead because the pearl sac is already formed

A bead-nucleated pearl is produced

1

2

3

4

5

BEAD NUCLEATION by DIRECT OPERATIONBEAD NUCLEATION by DIRECT OPERATION

Figure 17. Some Chinese pearl farmers use a direct (orD) operation modified from a similar process used toproduce saltwater cultured pearls in the South Seasand Tahiti. After removing the tissue-nucleated FWCP,the technician inserts a shell bead nucleus into theexisting pearl sac to grow another pearl. Mantle tissueis not needed in this case because the pearl sac isalready formed. Adapted from Li (1997).

from both Chinese and American freshwater mus-sel shells; Mr. Thengs factory uses the same trian-gle mussel in which the freshwater pearls are cul-tured as the shell for beads, too. We are aware thatshells cut from other mussels, such as Lamprotulaleai, are also used for bead cultivation in China (D.Fiske, pers. comm., 2001). To fashion the nuclei(typically 57 mm in diameter), PenfeiYouhezenzhu Co. uses machines imported from

Japan and the same procedure as is used in Japan.These beads are also exported to other pearl-produc-ing countries such as Japan and Tahiti.

Reports in the trade literature have suggestedthat some bead nuclei are made by grinding tissue-nucleated FWCPs into a round shape (Matlins,1999; Roskin, 2000). In our visits with a Chinesenucleus manufacturer and numerous pearl cultur-ers, we found no evidence of the commercial man-ufacture of such nuclei. Recently, one of theauthors (SA) asked a Japanese nucleus manufactur-er to fashion such nuclei from tissue-nucleated 10mm potato FWCPs to examine the appearanceand potential effectiveness of such a bead. By theusual shell-bead manufacturing procedure, theFWCPs were ground to round. The result was notsatisfactory, because the nacre peeled unevenlyduring grinding to produce a poor sphere.

CHARACTERISTICS OF CHINESE FWCPsMaterials and Methods. As described in the intro-duction, Chinese FWCPs are distinctive in terms ofsize, shape, color, and luster. Their internal struc-ture also is unique. To study these characteristics,two of the authors (SA and LTZ) examined approxi-mately 500 sample Chinese FWCPsranging from2 mm to 13 mm (figure 20)that were selectedfrom the stock (about 100 kg) of Stream Co. Theseare representative in color and luster of the better-quality cultured pearls being sold in China at thistime. The stock was harvested from a few Zhujiand Shaoxing pearl farms in July 2000. The buyersat Stream Co. purchased all of these samples as tis-sue-nucleated FWCPs; only a few farms in theseareas culture bead-nucleated FWCPs.

All of the pearls were examined visually by twoof the authors (SA and LTZ). Approximately 50 tis-sue-nucleated FWCPs were cut in half so that wecould examine the internal structure with a loupe.

Structure. Because the vast majority of ChineseFWCPs are tissue nucleated, solid nuclei are notnormally seen. Most of the sawn tissue-nucleatedFWCP sections showed traces of the tissue nucleusat the center, although in some samples they weredifficult to discern (figure 21). For this reason, as dis-cussed in depth in Scarratt et al. (2000), the separa-tion of natural from tissue-nucleated cultured pearlsis best done with X-radiography (see Appendix A).The cross-sections of the more strongly coloredsamples also showed distinct concentric color bands


Figure 20. Commercial round Chinese FWCPs rangefrom 2 mm to over 13 mm. The sizes of tissue-nucle-ated FWCPs are closely related to the culturing peri-od: 2 mm FWCPs such as the one on the far left can

be produced by a culturing period of less than twoyears, but the 13 mm FWCP on the far right typical-ly requires more than six years. Note also the range

of colors and the metallic luster in some of thesesamples. Photo by Li Tajima Zansheng.

Figure 19. To produce FWCPs over 10 mm, somecultivators insert larger (812 mm diameter) butfewer (usually one or two) bead nuclei togetherwith pieces of mantle tissue into the body of themussel under the liver and/or the heart. Adaptedfrom Li (1997).

between nacreous layers. These bands seem to berelated to the same mechanism that produces thevarious colors observed in the shell nacre of thehost H. cumingi mussel (figure 22).

Shape. In the past, Chinese FWCPs were typicallyelongated and wrinkled or pitted (again, see figure3). Although most Chinese FWCPs continue tobe oval or other shapes, the improvements in cul-turing techniques described above (e.g., the use ofyounger, thinner pieces of mantle tissue that canbe rolled into a ball) have brought a greater num-ber of round and near-round FWCPs to the mar-ketplace (figure 23).

Today, the most popular shapes are round, near-round, oval, button, drop, semi-baroque, and otherssuch as sticks and crosses. This wide variety ofshapes is characteristic of FWCPs from sourcesaround the world. The group we examined werespecifically selected to be round to near round.

Color. Chinese FWCPs occur in three main hueswhite, orange, and purpleall of which were repre-sented in our sample. Combinations of tone andsaturation yield a broad range of color appearances(figure 24) from which very attractive and distinc-

tive jewelry has been fashioned (figure 25). Pearldealers have described some Chinese FWCPs aswine, cognac, lavender (figure 26), blueber-ry, and apricot. This color range is believed tobe associated with: (1) the color of the mother-of-pearl in the donor mussel from which the piece ofmantle tissue was taken, (2) the environmentalconditions of the culturing farm, and/or (3) the age


Figure 23. The new tissue-nucleation techniquesbeing used in China have led to a greater numberof round freshwater cultured pearls in the market-place. Photo by Shigeru Akamatsu.

Figure 21. The evidence of tissue nucleation inChinese FWCPs can be very subtle. In most ofthese four tissue-nucleated samples, the nucleuscan be seen as a fine line toward the center of thesphere. Because such sawn sections are a highlydestructive means of identifying the type of nucle-us, and even they may not reveal the necessary evi-dence (if, for example, the tissue nucleus is slightlyoff-center), X-radiography is the best method toseparate tissue-nucleated cultured pearls fromtheir natural or bead-nucleated counterparts.During cultivation, growth rings of different colorsform in some FWCPs. Photo by Shigeru Akamatsu.

Figure 22. When the periostracum (the outer layerof the shell) of the triangle mussel H. Cumingi isremoved, the beautiful color and luster of thenacre are revealed. Insertion of mantle tissue takenfrom the posterior of the mussel into the posteriorof the live mussel is the key to producing bettercolor and luster. Photo by Shigeru Akamatsu.

of the host mussel. The first of these probably hasthe greatest effect on the color of an individualFWCP (Li and Zhang, 1997).

Luster. Our sample Chinese FWCPs demonstrated awide range of luster, from dull and chalky to metal-lic. On the basis of on-site investigations and inter-views with several cultivators in Shaoxing, two ofthe authors (SA and LTZ) concluded that the fol-lowing four factors can influence the luster ofChinese FWCPs:

The nature of the piece of mantle tissue used The location in the mussel where the tissue

piece is inserted The age of the mussel that has been nucleated The environmental conditions of the culturing

farm

As an example of this last item, experienced cul-tivators know that the water quality at Shaoxingpearl farms is different from that of pearl farmsalong the Chang Jiang River.

Pearl farmers carefully choose mussels with shellnacre that shows good luster as the source of themantle tissue to be used in the nucleation process.As noted above, to achieve the best luster (andcolor), the technicians insert the pieces of tissue intothe posterior of the mantle lobe. This region of themantle also experiences the most growth. A youngmussel bears lustrous pearls, but as it becomes older(more than five or six years), the luster of the pearlgradually decreases as its size increases. Pearl cultur-ers claim that the water quality (probably the differ-ence in mineral content) of their farms is the key toproducing pearls with a shiny metallic luster, butthat regardless of the farm the metallic luster willdisappear if the cultured pearl is left in a mussel thatis more than five or six years old.

In addition to these four factors, the musselspecies itself will affect pearl luster. Pearls withvery fine luster are produced when the pieces ofmantle tissue are cut from the mantle of a C. plica-ta and inserted into the mantle of an H. cumingi.However, almost all of the pearls produced withthis combination have heavy surface wrinkles.

CONCLUSIONAnnual production of freshwater cultured pearls inChina is estimated at about 1,000 tons, with approxi-mately 650 tons usable in the jewelry trade. However,the present expansion of cultivation indicates a sub-


Figure 25. This contemporary jewelry takes advan-tage of the combination of unusual colors offered

by Chinese FWCPs. Jewelry courtesy of StreamCo.; photo A.Takagi/Bexem Co. Ltd.

Figure 24. Chinese FWCPS occur in different tones,saturations, and combinations of white, orange,

and purple. Photo by Li Tajima Zansheng.

stantial increase within the next two or three years.Although more high-quality FWCPs are being pro-duced as cultivation methods improve, most of theChinese FWCPs are still of moderate to low quality.

The improvements in size, shape, surface condi-tion, luster, and color seen in recent years are theresult of many advances in the culturing materialsand techniques used. These include changing mus-sel species from C. plicata to H. cumingi, nucleationof younger (one-year-old) mussels, improvement inthe tissue nucleation (rolling a thinner piece of man-tle into a round shape and inserting fewer pieces intothe host mussel), a relatively longer culturing period,and a frequent change of culturing farms.

Bead-nucleation techniques also are being devel-oped, but our experience indicates that bead-nucle-ated FWCPs continue to represent a very small per-centage of the total production in China. Thisappears to be due to the technical difficulties andculturing costs involved. For example, bead nucle-ation doubles the labor required because both a beadand a piece of tissue must be inserted into the pock-et, whereas tissue nucleation requires only a singleaction to insert the piece of tissue. In any event, asdiscussed in Appendix A, the separation of bead-nucleated from tissue-nucleated cultured pearls, andof the tissue-nucleated product from its naturalcounterparts, is readily accomplished with contem-porary X-radiography techniques.

While this information represents the study ofseveral pearl operations and hundreds of FWCPs,the fact that China has many thousands of pearlfarms and produces tons of cultured pearls annuallymakes it impossible to provide a complete story.We believe, however, that the information we haveprovided is representative of the Chinese productseen in the market today and that the new nucle-ation and culturing techniques promise an even bet-ter product in the future.


Figure 26. Lavender is one of the distinctive colorsin which Chinese FWCPs occur. The rounds in thestrand are approximately 9.5 mm in diameter; thecultured pearl in the ring is 12.3 mm. Photo Harold & Erica Van Pelt.

ABOUT THE AUTHORS

Mr. Akamatsu is former manager of the Pearl ResearchLaboratory and currently general manager of the SalesPromotion Department, K. Mikimoto & Co. Ltd., Tokyo, Japan.Mr. Li, who started his Chinese freshwater cultured pearl busi-ness in 1985, is president of Stream Co., Tokyo and HongKong; in 1998, he established a pearl-processing operation inZhuji City, China. Mr. Scarratt is laboratory director at theAGTA Gemological Testing Center, New York; and Mr. Moses is vice president of Identification Services at the GIA Gem TradeLaboratory, New York.

ACKNOWLEDGMENTS

The authors express heart-felt appreciation to He Xiao Fa, directorof Shanxiahu Pearl Co. Ltd. in Zhuji City, and Lou Yong Qi, direc-tor of Echolou Pearl Co. in Zhuji City, for giving them the opportu-nity to visit several pearl farms, and for providing numerous FWCPsamples. The authors also gratefully acknowledge Mikio Ibuki, executive manager of the Japan Pearl Exporters Association(JPEA), for supplying Kasumiga cultured pearls. Last, the authorsthank Katsumi Isono, president of Miyake Nucleus ManufacturingCo. in Matsubara City, Osaka, for fashioning bead nuclei from tis-sue-nucleated potato FWCPs for the purposes of this research.


Cultured pearls form a significant portion of all gemmaterials traded. Yet the one nondestructive methodthat can be used to identify the growth technique orseparate cultured from natural pearlsX-radiogra-phyis available only to a limited number of gemol-ogists who have access to the necessary equipment.Nevertheless, it is important that all gemologistsunderstand the principles behind X-radiography andits capabilities in pearl identification. While the gen-eral method and operating procedures have been pub-lished by, for example, Webster (1994) and Kennedy(1998), this box provides specific information regard-ing the use of X-radiography in the identification offreshwater cultured pearls (FWCPs) grown by a vari-ety of techniques in China. The information is basedon the experience of two of the authors (TMM andKS) with taking and interpreting tens of thousands ofpearl X-radiographs over the last two decades, manyof which were of Chinese FWCPs.

Pearl Structure. Both natural and cultured freshwaterpearls are formed of concentric layers, of variablethickness, that are comprised of aragonite and/or cal-cite along with some organic matter. As the pearlgrows, more organic matter may be accumulated dur-ing one period than another, as seen in figure A-1.Some pearlsnatural or cultured by tissue nucle-ationhave a growth structure similar to thatbetween points A and B in figure A-1, whereas othershave one similar to that between points B and Cthroughout. Most Chinese freshwater cultured pearls(FWCPs) that are nucleated only with tissue also con-tain a characteristically shaped cavity near their cen-ter. If such samples are sawn adjacent to this cavity, itmay reveal itself only as a fine line (figure A-2). For amore complete explanation of the growth structure ofpearls, see chapter 22 of Webster (1994).

To better understand the identification criteriadiscussed below, it is important to note the less obvi-ous organic layers between points B and C in figureA-1, as well as the obvious ones. Note also the con-centric growth between A and B in figure A-1, and thestructures in figure A-2.

X-radiography Equipment. For more than 70 years,X-radiography has formed the backbone of pearl iden-tification. Fortunately for the industry, there are anumber (albeit limited) of gemologists with exten-sive experience in producing and interpreting X-radiographs. Although pearl X-ray units have gonethrough many incarnations, today there are severalindustrial units that are well suited to perform thetasks required for Chinese FWCP identification.

While we recognize that the latest digital or similarX-radiography units give the user a degree of conve-nience, it is the experience of these authors (TMMand KS) that the identification of Chinese FWCPsrequires a resolution that at this time is availableonly through the use of very fine-grain X-ray filmwet radiography. The instruments used by theauthors are Faxitron models 43855B and 43856A.These air-cooled units are powered by normal electri-cal outlets, have variable kV and mA control, andoffer an extended timed exposure capability. The dis-tance between the X-ray tube target and the sampleis adjusted by moving the shelving under the pearls.

Procedures. The samples should be placed in directcontact with a sheet of high-resolution fine-grainindustrial X-ray film; the film and the as-yet-uniden-tified pearls are then placed in a positionand at adistancethat will allow all the samples to be con-tained within the X-ray beam (figure A-3). Next,depending first on the size of the pearls, X-rays aregenerated for a specifically timed exposure at prede-termined kV and mA settings. Then, based on theinternal structures observed in the resulting X-radio-graph, the technician may increase or decrease the

APPENDIX A: IDENTIFYING CHINESE FRESHWATERCULTURED PEARLS BY X-RADIOGRAPHY

Figure A-1. In this thin section of a natural freshwaterpearl, the center of the pearl is located at the top left(A). Note the various stages of growth along the lineA-B-C. Between A and B is an evenly depositedarrangement of concentric layers, inside of which areradially arranged crystals. At B the structure abruptlychanges, with a large organically lined void that isfollowed by several yellow and dark, mostly organic,layers interspersed with the more crystalline (gray)layers toward the edge of the pearl (C).

A

B

C


exposure times, target-to-pearl distances, and kV andmA settings.

All X-radiographs are normally examined at mag-nifications between 2 and 10 (hence the need forfine-grained film) using a variety of back-illumina-tion techniques. The X-radiograph may show one ormore of the following features, depending on thenature of the sample:

1. If the sample was a coherent solid composed ofaragonite or calcite, without any organic mat-ter: The image would be simply an opaquewhite disc against a black background. That is,the aragonite or calcite would have absorbed theX-rays and left the film immediately below itunexposed (white), whereas the remainder of thefilm would have been fully exposed and thusblack when processed. This is how the shellbead portion of a bead-nucleated cultured pearlwould look, and is not uncommon for a non-nacreous (e.g., conch) pearl.

2. If the sample was aragonite or calcite with inter-nal organic material or voids: The image wouldreflect the difference in the ability of the X-rays topass through the aragonite or calcite, the organicmaterial, and any voids present. Organic layers andvoids pass X-rays more readily than calcium car-bonate does, so they reveal themselves on the pro-cessed X-ray film as dark gray to black lines orshapes set against the white background of the cal-

cium carbonate. If voids are present, the contrastbetween these and the calcium carbonate general-ly will be greater than that for organic material.

If one takes the more familiar example of ahuman bone contained within the flesh of thehuman body, a similar principle applies. The humanbone absorbs the X-rays more than the flesh that sur-rounds it and thus stands out clearly as whiteagainst the gray to black areas that comprise the flesh(organic). In addition, any fractures or fissures in thebone (voids) will appear black on the processed film.

Once the initial observations have been complet-ed, the technician takes additional X-radiographs,now optimized for the suspected type of pearlnatu-ral, cultured (bead or tissue nucleated), etc.beingexamined, in several different directions, to provideimages that can be interpreted as characteristic of thesample in three dimensions.

The scattering of X-rays as they pass throughand around a pearl may at times reduce the qualityof the image. Two techniques that the authors havefound to be successful in absorbing the scattered X-rays (and thus enhancing the image) are: (1) fornecklaces, immersing the pearls in a scatter-reduc-ing fluid; and (2) for single pearls, surrounding thesides of the sample with a thin layer of lead foil.

Characteristics of Tissue-Nucleated and Bead-Nucleated Chinese FWCPs. X-radiographs of tis-sue-nucleated FWCPs will show features thatdepend to some extent on when they were grown.Rice Krispie tissue-nucleated Chinese FWCPsgrown in the 1970s typically have somewhattwisted internal organic structures and voids (fig-ure A-4, left). X-radiographs of more recentlygrown tissue-nucleated Chinese FWCPswith

Figure A-2. In this sawn half of a knowntissue-nucleated cultured pearl, the slight dark linein the center (at B) is the only visual evidence of thetissue implant. Note, however, as in figure A-1 thevarying amounts of organic material (dark) associ-ated with the concentric growth structures.

A

B

C

Figure A-3. The samples (here, a baroque strandranging from 12.0 9.15 to 15.20 11.15 mm) areplaced on the film immediately below the X-raybeam in the Faxitron unit. Photo by E. Schrader.


their characteristic implant lineswere publishedby Scarratt et al. (2000; figure A-4, right). In bothcases, the X-radiographs are totally unlike those ofeither natural pearls (figure A-5) or of culturedpearls produced from a shell bead nucleus.

The X-radiographs of shell bead-nucleatedChinese FWCPs resemble those of shell bead-nucleated saltwater cultured pearls (figure A-6).Centrally located beads with no internal growthstructures are separated from the nacre overgrowthby a layer that is mostly organic. Any possible con-fusion with tissue-nucleated FWCPs caused bydark areas on the X-radiograph inside the area ofthe central bead would be dispelled by X-radio-graphs taken in other directions.

The X-radiographs of wax bead-nucleatedChinese FWCPs also show characteristic features(figure A-7). Each contains a nearly circular centralarea that is black or dark gray. Additional layers aredefined by fine black concentric growth structureswithin the white crystalline areas of the ChineseFWCP (which are not visible in figure A-7). Thereare similarities between the X-radiographic struc-

tures seen in this type of Chinese FWCP and thosesometimes observed in natural pearls. However, nat-ural pearls differ from Chinese FWCPs in that theyshow additional structures within the central area.

The short descriptions given here about the equip-ment needed, procedures, and expected results mustbe supplemented by operator experiencethe mostimportant element.

Figure A-6. This radiographic image of shell bead-nucleated Chinese freshwater cultured pearls istypical of the images seen for this product.

Figure A-5. Natural pearls typically do notshow evidence of a nucleus, only the structuresthat indicate organic matter or voids. Notealso the concentric rings throughout this pearl.

Figure A-7. Recently produced wax bead-nucle-ated Chinese FWCPs have the characteristicradiographic structures shown here.

Figure A-4. The dark graytwisted structures shownon the left are typical of thetissue-nucleated ChineseFWCPs produced in the1970s. In the X-radiographon the right of more recentFWCPs, ovoids mark theoriginal tissue implant.


REFERENCESBosshart G., Ho H., Jobbins E.A., Scarratt K. (1993) Freshwater

pearl cultivation in Vietnam. Journal of Gemmology, Vol. 23,No. 6, pp. 326332.

China producing nucleated rounds (1995) Jewellery News Asia,No. 129, pp. 5658.

China starts pearling revolution (2000) Jewellery News Asia, No.186, p. 62.

Farn A. (1986) Pearls: Natural, Cultured and Imitation.Butterworths, London, p. 76.

Fukushima Y. (1991) The freshwater pearl in China. Pearls of theWorld II, Les Joyaux special edition, Shinsoshoku Co., Tokyo,pp. 127134.

Hnni H. (2000) Gem news: Freshwater cultured Kasumigapearls, with Akoya cultured pearl nuclei. Gems &Gemology, Vol. 36, No. 2, pp. 167168.

Hiratsuka T. (1985) The Chinese freshwater pearl. Pearls of theWorld, Les Joyaux special edition, Shinsoshoku Co., Tokyo,pp. 95100.

Jobbins E.A., Scarratt K. (1990) Some aspects of pearl productionwith particular reference to cultivation at Yangxin, China.Journal of Gemmology, Vol. 22, No. 1, pp. 315.

Kennedy S.J. (1998) Pearl identification. Australian Gemmolo-gist, Vol. 20, No. 1, pp. 219.

Li H.P., Zhang X.P. (1997) Chapter 4: Nucleating operation. InDanshui Zenzhubang Yangyu [Freshwater Pearl MusselCultivation], Science Technology Literature Press, Beijing, pp.

3667 (in Chinese). Li S.R. (1997) Chapter 2: Nucleus Inserting Operation, 2Bead

nucleus inserting operation. In Danshui Zenzhu Peiyu Jishu[Freshwater pearl cultivation technique]. Jin Dun Press,Beijing, pp. 7178 (in Chinese).

Matlins A. (1999) Large Chinese freshwater cultured pearls.Journal of the Accredited Gemologists Association, Winter9900, pp. 1, 3, 5.

Roskin G. (2000) Are freshwater Chinese pearls being misrepre-sented? Jewelers Circular Keystone, Vol. 171, No. 3, pp. 36, 38.

Scarratt K., Moses T., Akamatsu S. (2000) Characteristics ofnuclei in Chinese freshwater cultured pearls. Gems &Gemology, Vol. 36, No. 2, pp. 100102.

Statistics of fishery and cultivation (2000) Almanac of FisheryAgency. Ministry of Agriculture, Forestry and Fisheries,Tokyo.

Toyama T. (1991) Freshwater pearlStatus of, and future. Pearlsof the World II, Les Joyaux special edition, Shinsoshoku Co.,Tokyo, pp. 119126.

Ward F. (1985) Pearl. National Geographic, Vol. 168, No. 2,August, pp. 192223.

Webster R. (1994) GemsTheir Sources, Descriptions andIdentification, 5th ed. Rev. by P.G. Read, Butterworth-Heinemann Ltd., Oxford, England, 1026 pp.

Wentzell C.Y. (1998) Cultured abalone blister pearls from NewZealand. Gems & Gemology, Vol. 34, No. 3, pp. 184200.

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TWENTY YEAR INDEX19812000

SPECTRAL REFLECTANCE ANDFLUORESCENCE CHARACTERISTICS OF

NATURAL-COLOR AND HEAT-TREATEDGOLDEN SOUTH SEA CULTURED PEARLS

114 GOLDEN SOUTH SEA CULTURED PEARLS GEMS & GEMOLOGY SUMMER 2001

first marketed in 1993 with full disclosure that theywere treated (Vock, 1997). Details of the proprietaryprocess are not known, but it has been reported thatthe treatment, which is believed to be stable, isapplied to undrilled cultured pearls and involves theuse of heat without the application of dyes orbleaching (Vock, 1997). Inasmuch as the report didnot exclude chemicals other than bleach, it is possi-ble that chemicals also may be involved in thetreatment. It is probable that other companies aretreating golden pearls using a similar process.

The challenge for the gem and jewelry indus-try is to separate natural-color cultured pearls, ofany color, from treated ones (Sheung, 1998).Although, as noted above, drilled treated culturedpearls generally can be distinguished from natu-ral-color cultured pearls by microscopy (Hargett,1989), undrilled cultured pearlsespecially in theabsence of obvious visual featuresare much

By Shane Elen

See end of article for About the Authors information and Acknowledgments.GEMS & GEMOLOGY, Vol. 37, No. 2, pp. 114123 2001 Gemological Institute of America

A comparison study was made between the yellow and white nacre of the gold-lipped Pinctada maximaoyster shell and 65 yellow cultured pearls, both natural and treated color, produced from this mollusk. Theyellow nacre of this shell has a characteristic absorption feature in the UV region between 330 and 385 nm;the strength of this feature increases as the color becomes more saturated. White shell nacre fluoresces verylight blue or very light yellow to long-wave UV radiation, whereas yellow shell nacre fluoresces greenish tobrownish yellow or brown. Natural-color yellow cultured pearls from P. maxima exhibited absorption andfluorescence characteristics similar to those of the yellow shell nacre. In contrast, the absorption feature inthe UV was either weak or absent in yellow cultured pearls reportedly produced by a method involving heattreatment, and their fluorescence was generally very light blue or light yellow.

he popularity of golden cultured pearlsfrom the South Seas (figure 1) has increasedsteadily over the last 10 years (Vock, 1997;

Prices of golden, 2000). As demand for thesecultured pearls has grown, treated-color goldencultured pearls have also entered the marketplace.A portion of the South Sea yellow cultured pearlsharvested are well shaped with few blemishes butwith less desirable coloreither very light(Federman, 1995) or uneven. The most commonmethods used to produce or enhance yellow col-oration in South Sea golden cultured pearlsinvolve treatment with a chemical or an organic dye.The fact that so many different chemicals and dyescould be used for this purpose complicates a compre-hensive study of these treatment methods.However, inorganic chemicals are routinely identi-fied using EDXRF; and dyes, since they usually areapplied after the pearls are drilled, generally are easyto identify with magnification.

The Ballerina Pearl Co. (New York City) devel-oped a method in the early 1990s to treat thesepoorly colored South Sea cultured pearls to producea more uniform and desirable yellow. These were

T

GOLDEN SOUTH SEA CULTURED PEARLS GEMS & GEMOLOGY SUMMER 2001 115

more difficult to identify. The present reportcompares heat-treated yellow cultured pearls tonatural shell nacre and natural-color yellow cul-tured pearls from the Pinctada maxima to identi-fy criteria that can be used to separate treatedfrom natural-color material, especially when thesamples are undrilled.

BACKGROUNDThe gold-lipped P. maxima oyster has a characteris-tic yellow to golden nacre inside the shell alongthe periphery of the white nacreous region (Gervisand Sims, 1992, p. 4; again, see figure 1). Pearls pro-duced from this oyster, either natural or cultured,are typically white, silver, or yellow (South SeaPearl Consortium, 1996) and include so-calledgolden pearls.

The post-harvest color treatment of culturedpearls, of any color, falls into two categories: prior todrilling and after drilling. Heat treatment (Vock,1997) and gamma irradiation (Ken-Tang Chow,1963) may be performed pre- or post-drilling. Asnoted above, however, dyes and chemicals typicallyare used only after drilling (Komatsu, 1999), to facil-itate their entry parallel to the nacre layers.Generally, such treatments affect the organic mate-rial (i.e., conchiolin) between the nacre layers; theyhave less influence on the crystalline nacre (Gau-thier and Lasnier, 1990).

The most obvious indication of these treatments(with the exception of irradiation) is an unusualcolor concentration in the form of a colored layer(visible in the drill hole) or a colored spot or streakvisible on the surface (Komatsu, 1999). Color fromdyes or chemicals typically becomes concentratedin surface defects such as cracks, pits, or blemishes(Newman, 1999, p. 94). Dimples or protrusions inthe nacre are particularly likely to exhibit concen-trations of color. These areas are often more porous(as indicated by a cloudy or milky appearance priorto treatment), which allows the dye or chemical tobecome concentrated (T. Moses, pers. comm.,2000). These features sometimes are eye-visible, butusually they can be detected only with microscopy.

Typically, detection of a treated yellow color inundrilled cultured pearls relies on the presence ofsurface color concentrations. When such featuresare absent, however, identification is more of a chal-lenge. Inasmuch as the Ballerina process is appliedprior to drilling, this is the situation for yellow cul-tured pearls treated by this technique.

Due to the nature of the chemicals and dyes typ-ically used in most post-drilling treatments, manycolor-treated natural and cultured pearls can beidentified using X-ray fluorescence (XRF) or Ramanspectrometry (see box A). However, the author didnot find these techniques useful for the heat-treatedgolden pearls tested for this study. Thus, the pur-

Figure 1. These nat-ural-color and heat-treated culturedpearls range from12.5 to 13.6 mm;the natural-colorcultured pearls areon the top right andbottom left. Notethe area of goldennacre along theperiphery of thewhite nacreousregion in the gold-lipped Pinctadamaxima shell (18.0cm in diameter).Photo by MahaTannous.

Figure A-1. The iodine (I) peaks in this energy-dispersive X-ray fluorescence (EDXRF) spec-trum of a yellow Akoya cultured pearl indi-cate chemical treatment.

Figure A-2. In this Raman spectrum of an orangyyellow Akoya cultured pearl, the series of peaksabove 1085 cm-1 indicate treatment with anorganic dye.

Figure A-3. In a UV-Vis (ultraviolet-visible)reflectance spectrum, an absorption maximumat 700 nm is characteristic of natural-colorblack cultured pearls from the Pinctada mar-garitifera oyster.

Figure A-4. This luminescence spectrum of a culturedblack pearl from Pinctada margaritifera shows fluo-rescence peaks at 617 and 676 nm due to porphyrins,which are responsible for the reddish brown fluores-cence to 365 nm UV or 405 nm blue light.


Advanced testing often can be used to identify color-treated cultured pearls. These techniques include X-ray fluorescence (XRF), Raman and luminescencespectrometry, and UV-Vis spectrophotometry. XRFis useful for detecting the presence of inorganictreatments such as silver salts (black) or iodine (yel-low; figure A-1). In most cases, organic treatmentsand biological pigments cannot be detected by thismethod, but their presence can sometimes be deter-mined using Raman spectrometry (figure A-2). UV-

Vis spectrophotometry frequently is used to identifythe presence of chromophores responsible for natu-ral coloring in Tahitian black cultured pearls, asindicated by an absorption at 700 nm (Komatsu andAkamatsu, 1978; figure A-3). Luminescence can ver-ify the presence of porphyrins (Miyoshi et al., 1987)responsible for the reddish brown fluorescenceobserved in natural-color black cultured pearls origi-nating from the Pinctada margaritifera, Pteria ster-na, and Pteria penguin oysters (figure A-4).

BOX A: ADVANCED IDENTIFICATION OF COLOR TREATMENTSIN NATURAL AND CULTURED PEARLS


pose of the present research was to determine othernondestructive spectral or fluorescence characteris-tics that could be used to aid in the identification ofheat-treated yellow cultured pearls from the P.maxima that either are undrilled or have drill holesthat are inaccessible for examination.

For convenience and brevity, natural-color yel-low cultured pearls will henceforth be abbreviatedas NYCPs, and reportedly heat-treated yellow cul-tured pearls as HTYCPs. Note, too, that the hue,tone, and saturation terms used to describe the col-ors of the shell and cultured pearl samples are basedon the new (2000) GIA pearl grading system.

MATERIALS AND METHODSTo establish the characteristics of known untreatedmaterial, we obtained a total of 42 samples of nacrefrom seven gold-lipped P. maxima shells that origi-nated from Australia (2 shells), the Amami Islands inJapan (2), and the Philippines (3). The samples, eachapproximately 9 mm in diameter, were removedwith a diamond saw while the shells were com-pletely immersed in water, since overheating couldaffect their color (Webster, 1994) and thus their fluo-rescence or spectral characteristics. Two samples ofwhite nacre and four samples of yellow nacre wereobtained from each shell, for a total of 14 whitenacre and 28 yellow nacre samples.

In addition, 53 NYCPs, ranging from 9.1 to 15.7mm, were obtained from several reputable sources.They were reportedly from Indonesia (5), thePhilippines (23), Japan (3), Australia (6), and theSouth Seas in general (16). Forty-five wereundrilled and eight were drilled. Twelve undrilledtreated-color yellow cultured pearls, which werereportedly heat treated, were also obtained for thestudy; they ranged from 11.8 to 13.1 mm. We believethat these samples originated from the gold-lippedvariety of the P. maxima; we could not confirmwhether the process has been applied to culturedpearls from the silver-lipped P. maxima. No strongly

saturated yellow cultured pearls of known pedigree,natural or treated, were available for characterization.

All of the cultured pearls were examined with aGIA Gem Instruments Mark VII microscope usingfluorescent and fiber-optic lighting. Initially sixNYCPs and six HTYCPs were analyzed with aRenishaw 2000 Ramascope laser Raman microspec-trometer and a Thermo Noran Spectrace 5000EDXRF spectrometer. Inasmuch as neither tech-nique revealed any distinct differences between thenatural- and the treated-color samples, further test-ing by Raman and EDXRF was discontinued.

UV-Vis reflectance spectra and fluorescenceobservations were obtained for each sample using aHitachi 4001 spectrophotometer and a UVP modelB100 AP long-wave ultraviolet lamp. Reflectancespectra were collected from 250 to 2500 nm,although only the pertinent data range (i.e., 250700nm) is illustrated in this article. At least two spectrawere obtained in different regions for each culturedpearl that showed uneven color or fluorescence dis-tribution. A total of 162 reflectance spectra werecollected: 42 on the shell nacre samples, 94 on thenatural-color cultured pearls, and 26 on the treatedcultured pearls. Acquisition of luminescence spec-tra with a Spectronic AB2 luminescence spectrome-ter was unsuccessful, due to instrument configura-tion, sample shape, and the generally desaturatedfluorescence colors. Therefore, fluorescence colorand distribution were observed visually in a dark-ened room with the aid of UV contrast goggles.

RESULTSVisual Appearance. Fourteen of the shell nacre sam-ples were white, and 28 ranged from light to darkyellow (see, e.g., figure 2). The natural-color cul-tured pearls ranged from very light yellow to orangyor greenish yellow (see, e.g., figure 3); a few exhibit-ed slightly uneven color distribution. The HTYCPsranged from light yellow to orangy yellow (see, e.g.,figure 4), with the majority being light yellow.

Figure 2. These five samples, each about 9 mm indiameter, show the range of color seen in thePinctada maxima shell nacre samples. Photo byMaha Tannous.

Figure 3. The natural-color yellow cultured pearlsranged from very light yellow to orangy (as shownhere) or greenish yellow. These pearls are 11.613.6mm in diameter. Photo by Maha Tannous.

Small, localized spots of concentrated color werevisible in 10 of the 12 HTYCPs, with either theunaided eye or magnification (figure 5). The remain-ing two did not exhibit any visible or microscopicevidence of treatment.

UV-Vis Reflectance Spectra and Fluorescence. ShellNacre Samples. The UV-Vis spectra revealed adecrease in reflectance due to absorption between330 and 460 nm for all 28 yellow shell nacre sam-ples as compared to the samples of white shellnacre. This broad region of absorption is actuallycomposed of two features: one in the UV regionfrom 330 to 385 nm, with a maximum between 350and 365 nm; and the other in the visible region from385 to 460 nm, with a maximum between 420 and435 nm. The spectra of the white shell nacre sam-ples showed no absorption features in this broadregion. Examination of the reflectance spectra for aseries of five samples that ranged from white todark yellow revealed an increase in the generalabsorption between 330 and 460 nm as the strengthof the yellow coloration increased (figure 6).

Typically, dark yellow shell nacre exhibitedmoderate brown, greenish brown, or greenish yel-low fluorescence, and light yellow shell nacre flu-oresced light brown or light yellow (see, e.g., fig-ure 7). Most of the white shell nacre samplesshowed moderate-to-strong very light blue fluo-rescence, although some appeared to exhibit aslight trace of yellow.

Natural-Color Cultured Pearls. The spectra forthese samples (figure 8) exhibited absorption charac-teristics similar to those of the yellow shell nacre,except that the maximum in the UV varied from350 to 385 nm. All but four of the 94 spectraobtained on these samples exhibited the two absorp-tion features between 330 and 460 nm. In the fourspectra that did not show these features, the regions

analyzed were white areas on unevenly coloredsamples; and these results were similar to thereflectance spectra obtained for white shell nacre.As the yellow color of the cultured pearls increasedin saturation, the long-wave UV fluorescence pro-gressed from light yellow or light brown, to greenishyellow, greenish brown, or brown.

Heat-Treated Cultured Pearls. Five of the 26reflectance spectra obtained from the HTYCPs


Figure 4. The heat-treated yellow cultured pearlsranged from light yellow to moderate orangy yel-low. The samples shown here are 11.312.6 mm indiameter. Photo by Maha Tannous.

Figure 5. Small spots of concentrated color are evi-dent within blemishes on this yellow culturedpearl that reportedly has been heat treated.Photomicrograph by Shane Elen; magnified 5.

Figure 6. These reflectance spectra of five shellnacre samplesranging from white through darkyellowshow increasing absorption from 330 to460 nm as the color intensifies. Note in particularthe increasing absorption in the UV region from330 to 385 nm.

exhibited a weak absorption feature in the UV regionaround 345 nm (see, e.g., figure 9). These spectra rep-resented five of the 12 treated cultured pearls stud-ied. Spectra taken from other areas on these samefive HTYCPs, and from the remaining sevenHTYCPs, exhibited very weak or no absorption inthe UV region. All 26 spectra showed an absorptionfeature in the blue region between 415 and 430 nm.

Generally, the fluorescence of the HTYCPs wasslightly uneven, and appeared unrelated to the dis-

tribution of bodycolor. In one HTYCP, however,fluorescence did appear to be related to the unevendistribution of the yellow color: Light yellow andlight brown fluorescence corresponded directly toareas of light yellow and light orangy yellow. Eightof the HTYCPs, which were light in tone and satu-ration, fluoresced moderate to strong light yellow;twoalso light in tone and saturationexhibited avery light blue fluorescence. The sample with the


Figure 8. As was the case with the shell nacre sam-ples, the reflectance spectra of the natural-coloryellow cultured pearls showed increasing absorp-tion in the 330460 nm region with greater satura-tion of color.

Figure 9. The reflectance spectra of the heat-treatedyellow cultured pearls revealed very weak or noabsorption in the 330 385 nm region. The presenceof a weak UV absorption feature around 345 nmsuggests that the orangy yellow cultured pearlexhibited some natural yellow coloration prior totreatment.

Figure 7. The typical fluorescence reactions of natural- and treated-color cultured pearls when exposedto 365 nm (long-wave) UV radiation are illustrated here. Shown in normal lighting (left in each pair)and with long-wave UV (right) are: (A) white shell nacre, (B) yellow shell nacre, (C) 13.6 mm natural-color light yellow cultured pearl, (D) 12.5 mm natural-color orangy yellow cultured pearl, (E) 12.6 mmheat-treated light yellow cultured pearl, and (F) 12.6 mm heat-treated orangy yellow cultured pearl.Normal lighting photos by Maha Tannous; fluorescence photos by Shane Elen.

A

B

C

D

E

F

most saturated orangy yellow bodycolor fluoresceda light brownish orange. The spots of concentratedcolor seen in some HTYCPs (see figure 5) fluoresceda strong orange to long-wave UV.

DISCUSSIONConfirmation of Reported Origin of Color. One ofthe main challenges of performing a study of thiskind is obtaining samples of known species andcolor origin. Ideally for pearls of natural color, wit-nessing the removal of the pearl from the oysterwould be the method of choice. However, this is notalways practical, so instead we must look to veryreliable sources. Similarly, obtaining pearls treatedby specific methods also can be very challenging.

None of the cultured pearls represented as beingof natural yellow color showed any visible indica-tions of treatment, whereas most of the culturedpearls reported to be heat treated did exhibit somevisible evidence in the form of spots with concen-trated color. In most cases, too, there was a distinctdifference in reflectance spectra between yellow

cultured pearls stated to be natural color and thosethat were reportedly heat treated. In addition, thosestated to be natural color exhibited reflectance andfluorescence characteristics similar to the samplesof shell nacre of similar color. These findings wouldappear to support the reported color origins for thecultured pearl samples used in this study.

Although no chemical study of the zoochrome (anaturally occurring pigment molecule found in theanimal kingdom; Needham, 1974) was performed,the reflectance and fluorescence results indicatethat the yellow coloration in P. maxima shells andNYCPs appears to be due to a common zoochromeregardless of their geographic origin.

Spectral Reflectance Characteristics. A broadabsorption between 330 and 460 nm in thereflectance spectra was seen in the yellow nacrefrom both the gold-lipped P. maxima shell and theNYCP samples (figures 6 and 8), and thus appears tobe characteristic of natural-color yellow nacre pro-duced by this species. The strength of this absorp-tion appeared to increase as the color became moresaturated. The 420435 nm maximum (in the blueregion of the visible spectrum) is typical ofreflectance spectra for yellow objects (Lamb andBourriau, 1995), and is responsible for the yellowcolor observed. Although UV absorption is not nec-essary to produce yellow coloration, it does appearto be related to the same zoochrome that is respon-sible for the absorption in the blue region of the visi-ble spectrum. The absence of this absorption maxi-mum in the UV reflectance spectra obtained fromwhite areas on unevenly colored cultured pearls isconsistent with the reflectance results obtained forwhite shell nacre.

The HTYCPs exhibited an absorption in theblue region, as would be expected for a yellow cul-tured pearl, but there was a significant difference inthe strength of UV absorption between similarlycolored natural and treated cultured golden pearls(figure 10). The absence of the UV absorption fea-ture in the HTYCPs indicates that the cause of theiryellow coloration is different from that of theNYCPs tested. The fact that some areas of the treat-ed cultured pearls showed a weak UV absorptionfeature suggests that these areas were a light yellowprior to treatment.

Ultraviolet Fluorescence. Fluorescence can be avaluable yet challenging identification technique,since many of the effects and color differences are


Figure 10. These reflectance spectra of natural andtreated light yellow (top) and orangy yellow (bot-tom) cultured pearls show a distinct difference inabsorption in the 330385 nm region. Note thelack of absorption in this region shown by thetreated-color samples.

quite subtle and can vary depending on the type oflong-wave UV source used. It is important toobserve the relationship between (1) the tonal distri-bution of the yellow color, and (2) the distributionand hue of the fluorescence (again, see figure 7). Forthe natural-color samples, the distribution of fluo-rescence matched the evenness or unevenness ofthe color distribution: An even yellow distributioncorresponded to an even fluorescence distribution,and uneven color showed uneven fluorescence. Aneven color distribution with a patchy fluorescenceis indicative of treatment. In lighter samples, how-ever, slight tonal variations in nacre color can bequite difficult to see compared to the more obviouspatchy fluorescence.

In addition, the fluorescence colors emitted byboth natural- and treated-color light yellow cul-tured pearls can be similar, and thus they are lessreliable as an indicator of treatment. The exceptionto this is the very light blue fluorescence observedin natural white nacre and in some light yellowHTYCPs. The fact that no NYCPs of light yellowcolor exhibited this fluorescence color would implythat the treated-yellow sample was originallywhite. (Caution must be observed, however,because some long-wave UV lamps emit enoughblue visible light to render this observation unreli-able.) The HTYCPs also lacked the greenish fluo-rescence component noted in many of the yellowshell nacre samples and NYCPs. Neither theNYCPs nor the yellow shell nacre exhibited thestrong orange fluorescence seen in the spots of con-centrated color of some of the HTYCPs; therefore,distinct spots of strong orange fluorescence wouldindicate treatment.

Inasmuch as the details of the heat-treatmentprocess are unavailable, the effect that heat treat-ment might have on the individual componentsthat contribute to fluorescence (i.e., conchiolin,aragonite plates, and pigments) was not investigat-

ed. It has been reported that the fluorescence of con-chiolin can be affected by certain treatments (S.Akamatsu, pers. comm., 2001). However, the differ-ences in fluorescence between natural- and treated-color cultured pearls may result from a combinationof these components and not necessarily from anyone component in particular.

Identification of Heat-Treated Yellow CulturedPearls. Table 1 summarizes key identificationcharacteristics for natural-color and heat-treatedyellow cultured pearls produced by the P. maximaoyster. As indicated below, the ease with whichHTYCPs can be identified depends greatly onwhether the original cultured pearl had even oruneven color.

1. An HTYCP that exhibited white and yellowareas prior to treatment is likely to be the easiestto separate from natural color. After treatment,the white areas would appear yellow but wouldexhibit the UV spectral characteristics of whitenacre; that is, the UV absorption characteristic ofyellow nacre between 330 and 385 nm would beabsent. In this type of treated cultured pearl, areasthat formerly were white fluoresce a lighter colorthan do the yellow zones. The uneven fluores-cence also may contrast with an even yellow col-oration of the treated cultured pearl.

2. An HTYCP that exhibited evenly distributed,very light color prior to treatment may exhibit aUV absorption feature that is too weak for itsapparent color (figure 10). Also, the fluorescencecolor might appear too light for the apparent toneand saturation of the treated cultured pearl.

3. Probably the most difficult to identify would beHTYCPs that were originally unevenly coloredlight and dark yellow. Nevertheless, this type ofHTYCP is likely to exhibit uneven fluorescence,possibly in contrast to an even yellow coloration.


TABLE 1. Summary of identification characteristics for natural-color and heat-treated yellow cultured pearls produced by P. maxima.

Nacre UV absorption Visible absorption Fluorescence to long-wave UV Commentscolor feature feature

(330 385 nm) (385460 nm)

Natural white None None Moderate to strong; very light Generally very light blue blue or very light yellow fluorescence

Natural yellow Distinct to strong Present Moderate; light yellow or light Even distribution of bodybrown, to greenish yellow, color will be accompanied greenish brown, or brown by even fluorescence

Heated yellow None to weak Present Moderate to strong; light yellow, Even distribution of body very light blue, or light brownish color may be accompaniedorange by uneven fluorescence

Again, the UV absorption feature would likelyappear too weak for the apparent color of thetreated cultured pearl.

If heat-treated cultured pearls are subsequentlydrilled, the color may appear to be concentrated inthe surface layers of nacre when observed throughthe drill hole (T. Moses, pers. comm., 2000).

CONCLUSIONAs golden cultured pearls from P. maximabecome increasingly popular in the marketplace(figure 11), there is growing incentive to treat off-color cultured pearls to produce these rich yellow toorangy yellow colors. As a result, the separation oftreated-color from natural-color pearls has become aconstant challenge for the gemologist. Althoughcolor treatment is relatively straightforward to iden-tify in many drilled cultured pearls because of dis-tinctive color differences in the layers visible

through the drill hole, certain treatmentsespecial-ly heat treatmentmay be very difficult to detectin some undrilled cultured pearls.

The present study of white and yellow shellnacre from gold-lipped P. maxima shells showed acharacteristic increase in absorption between 330and 385 nm in the UV spectrum as tone and satura-tion increased from white to dark yellow. Thisabsorption appears to be related to the zoochromeresponsible for absorption in the blue region, whichresults in the yellow color of the nacre. The changein absorption with increasing tone and saturationwas accompanied by a similar change in long-waveUV fluorescence, which progressed from very lightblue or very light yellow, to light yellow or lightbrown, to greenish yellow, greenish brown,

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