Robert Crowningshield's Insights into Pearl Cultivation (published in 1962)

Freshwater Pearls

The Laboratory examination of baroque, oval and round freshwater cultured pearls without mother-of-pearl centers was reported in Gems & Gemology, Summer 1958, at about the same time that hollow-centered Australian cultured pearls were described. Prior to this, we had seen in the New York Laboratory small, very flattened, baroque freshwater cultured pearls and reported them in The Loupe, January-February, 1958.

Very pleasing and marketable freshwater cultured pearls became available to the American market in quantity in 1961, when the Jahawa Corporation, 580 Fifth Avenue, NYC, was formed, as the exclusive United States distributor. Since little has been published about these pearls and because new sources of information have become available, it seems a good time to note developments in the cultured-pearl industry, with a view to discussing terminology and developing an understanding of the relatively unknown process whereby pearls may be grown in fresh-water mussels or clams without the use of a bead nucleus.

Highlights of Cultured-Pearl Production

Most readers are familiar with the long history of the attempts to encourage various molluscs to produce pearls. Many of these efforts (in fact, all the early ones) were carried out with freshwater molluscs variously called mussels or clams. The earliest work was that of the 13th century Chinese, whose method of placing small lead images, usually of Buddha, inside the mussel shells is well known.

A Swedish botanist (Linnaeus) did considerable work with mussels in the 170()'s, though ingenious, his method never resulted in commercially grown pearls. Dr. Kunz, in his Book of the Pearl, states that, in 1900, there was a considerable industry in China of making "culture" pearls with mother-of-pearl or porcelain beads placed inside the shells of a common mussel indigenous to the rivers in Chekiang Province. He states that at about this time the Japanese efforts were producing better "culture" pearls than those of the Chinese, only the Japanese were using salt-water molluscs.

Dr. Kunz mentions in his book (published in 1908) the work of Mikimoto and his cultured blister pearls (mobe pearls) , but he accords T. Nishikawa, rather than Mikimoto, the honor of producing the first cultured pearl.

 However, according to A. R. Cahn, in his very important 1948 report, Pearl Culture in Japan, the first spherical cultured pearl was made by Tatsuhei Mise, using mantle-tissue grafts and lead pellets in the Pinctada martensii. The date given by Dr. Cahn was 1904. Mise was evidently the first to appreciate the necessity of introducing epithelial mantle tissue, along with the nucleus, into the connective tissue of the mollusc in order for a pearl sac to form. Due to difficulties in unraveling Japanese patent information, it seems that T. Nishikawa, later Mikimoto's son-in-law, was actually granted a patent for spherical cultured-pearl production before Mise, but it was granted just seven weeks after one was issued to Mikimoto. It would appear, too, that patent applications often lay dormant in the patent office in Tokyo, since Nishikawa had made an application in 1907 and the patent was not granted until 1916.

In practice, it was Nishikawa's method of inserting a small bit of mantle tissue along with the nucleus, rather than Mikimoto's complicated method, that was adopted and has led to the present cultured-pearl industry in Japan, Burma and Australia. Mikimoto's method required sewing up the nucleus in a tiny square of mantle tissue prior to insertion. Attempts to cultivate pearls without mother-of-pearl nuclei were made over many years. At least one patent (to K. Mikimoto, in May, 1936) was granted for a method of making "non-nucleated pearls," using a thin "mud" made of pulverized shell or other materials mixed with epithelium from the mantle of another pearl oyster and sea water. This was claimed to be successful in initiating pearl formation when placed inside the body of the "mother" pearl oyster. It is assumed that the method was never successfully used commercially.

In Japanese waters the most successful mollusc for pearl culturing is Pinctada martensii, which, unfortunately, does not produce a large shell. Mature individuals may reach four inches in diameter, but the average is about three inches.

Possibly, because of this, culturists gave some attention as early as the late 1920's to the large fresh-water clam, or mussel, Hyriopsys Schlegeli (Figure 4), called Ikechogai in Japan. It may attain a length of nine inches. It is found along the eastern and southern shores of Japan's largest lake, Biwa-ko. (ko is the Japanese generic word for lake.) The lake, covering about 180 square miles, lies approximately ten miles northeast of Kyoto, in Shiga Prefecture.

Early attempts to adapt the salt-water culturing techniques, using large mother-of-pearl nuclei, met with little success, because of the involved and twisted intestine that complicates the internal anatomy of the mollusc. Operated animals that did not immediately die from the nucleus insertion usually formed discolored, poorly shaped or non-lustrous pearls. A large percentage of the growers abandoned hope of finding a larger mollusc in Japanese waters and turned their attention farther afield, both before and after World War II.

They experimented with some success with the warm-water relatives of Pinctada Martensii, such as Pinctada margaritifera and Pinctada Maxima. Since the War, Mergui Bay, oft Burma, as well as Australia's northern shore, have been the main areas for culturing large molluscs for accepting large nuclei. Although the large, fresh-water clam in Lake Biwa was not at first successfully used for nuclei insertion, certain experimenters did not give up hope of using the mollusc for culturing operations.

Just before the War, the work was conducted solely under the direction of Mr. Seiichiro Uda, president and director of the Shinko Pearl Co., Ltd. Mr. and Mrs. Uda visited both of the Instituters offices in the fall of 1961, and staffs of the Los Angeles and New York Laboratories are indebted to him for information heretofore unavailable. Today, there are more than thirty producers on Lake Biwa, not all of whom follow the procedures outlined hereafter. The producers are banded together in an organization, the Shiga-ken Fresh-Water Pearl Fishery Association, of which Mr. Uda is president.

Unlike the salt-water culturing operations, there is no need at the present time to propagate the clams artificially. However, the life history of the clam is being studied so that, in the future, if it becomes necessary, the growers will be prepared. It has been reported that the clams spawn in June and July. The eggs attach themselves to fish and begin their growth, later falling to the lake bed. A combined mud-and-sand bed has been determined to be the most satisfactory for the growth of the young clam. They are considered to be of operable size when they attain a length of approximately five inches. They are gathered from October to April by local fishermen who drag a kind of bottom trawl net that has been equipped with a rake fitted across its mouth. The molluscs are about three-fourths submerged in the lake bed during the gathering months. The rake prongs are spaced so that only clams of a certain size are gathered. The gathered clams are sold to the several pearl growers who place them in retaining pens; here they stay until ready to be operated on.

Although pearls usually are grown without nuclei in the fresh-water clams, the principle of a pearl sac is used. Today, the procedure is to bring the clams from the retaining pens to a building where girls trained in the work peg the two shells open and expose the mantle. Now, unlike the salt-water procedure, which requires an incision to be made in the fleshy gonad tissue, the girls make ten incisions in each half of the mantle. Into each small cut a piece of mantle tissue previously prepared from another clam is inserted and carefully pressed into position. It is in this incision that the mollusc forms a pearl sac in which a pearl grows.

Prior to about ten years ago, before it was discovered that the main body of the animal need not be disturbed, bits of mantle from the clam being operated on were pressed into from six to ten places in the gonad with a special forceps. Only very baroque and often poorly colored objects resulted.

After the graft operation, the clams are placed in plastic baskets that are suspended about three feet below the surface of the lake. In reality, the area is only an arm of the lake that has a more or less constant water level, thanks to a low dam and dikes across a narrow section of it.

Periodically, the baskets are raised and inspected, the dead clams removed, and foreign growths cleaned away. At least in fresh water, there is an absence of the scourges that plague the salt-water culture farms, i.e., star fish and the red tide. And, in addition, there is greater protection from typhoon and storm conditions. At the end of three years, the clams are returned to the plant, where the pearls are carefully removed with tweezers. Although only about 60% reach this stage, nearly 100% of these bear their full quota of twenty pearls each.

The life span of Hieryopsis schlegeli is about thirteen years, nearly twice that of the salt water pearl bearer, Pinctada martensii; therefore, it has been found that if the molluscs are returned to the water after the removal of the first "crop," a second crop will grow! Some animals in good condition have been known to bear even a third crop. We failed to find out why the growth period is interrupted after only three years, but presume it is due to the characteristics of the pearls when left longer.

It is claimed that freshwater cultured pearls are saleable without need for any of the various bleaching or dyeing processes reportedly used for the nucleated pearls from salt water. The first crop produces pearls usually of very baroque or oval shape, whereas the second crop tends to be much more spherical. No data was available on the quality of the third crop.

Quality of the Production

Mr. Uda stated that the pearls are usually more lustrous and of a darker color than the inside of the shell in which they grew; this is borne out by samples we have seen. The colors of these "tissue-graft, cultured fresh-water pearls" vary from almost white with a slight rose overtone to pastel shades of pink, orange, cream, bluish and, more rarely, greenish. To a specialist in freshwater pearls, their color and textures are reminiscent of natural fresh-water pearls of North America and thus, to his eye, distinguishable from pearls from the Persian Gulf.

At this writing, the oval pearls attain a maximum size of approximately 7 1/2 mm long, whereas the more nearly round pearls seldom exceed 6 mm. It is quite possible that, as the process continues to be improved, even larger and better-shaped pearls will be produced. In the five years that has elapsed since we saw our first small, flattened but lustrous baroques until today, a tremendous improvement has taken place. Mr. Uda says that he has been using the "pearl-sac-in-the-mantle" technique for about ten years. Efforts to grow large nucleated pearls in H. Schlegeli are, according to Mr. Uda, limited mainly to experimentation. Nevertheless, we do see necklaces and some lots of pearls up to 10 mm. in diameter). Most have a creamy light-orange color, good luster, but a somewhat irregular round shape.

Some pearls have cores that were drilled prior to insertion and that the completed pearls, when drilled, show no relationship between the final drilling and the drill hole in the nucleus. Earlier, we had assumed that discarded beads were used ,but Mr. Uda stated that the operators had found drilled nuclei necessary when using a special device for locating the nucleus in a non-vulnerable spot within the body tissues. Many of these nucleated pearls are of a dark and unpleasing color, therefore, it may be true that, commercial possibilities for this type of growth are limited.

IdentifIcation of Fresh-Water Cultured Pearls

As mentioned before, the bulk of the pearls grown in Lake Biwa are produced by the insertion, not of a solid nucleus, but of a bit of mantle tissue that initiates the production of the necessary pearl sac within the host's mantle. Therefore, we see in the X-radiograph of all but the roundest pearls a more or less oval to vermiform shadow, which has been found to vary from a large to a very thin hollow space when the pearls are then sectioned. This pattern, together with the strong fluorescence under X-rays of all fresh-water pearls and the almost total lack of fluorescence under long ultraviolet irradiation, is taken as proof of fresh-water cultured pearls. In the case of the round to nearly round second-growth cultured pearls, the pattern in the X-radiograph may be indistinguishable from an ordinary natural pearl, however, the fluorescence characteristics serve to identify these pearls. The baroque pearls frequently show a very large hollow space. The identification of the nucleated pearls depends on the normal radiograph used for any mother-of-pearl-nucleated cultured pearl and offers no difficulty.

Freshwater Cultured-Pearl Terminology

Terminology for the tissue-graft cultured fresh-water pearls requires some clarification. Obviously, both the nucleated and the tissue-graft methods of initiating pearl growth are "caused or induced by man" the criterion mentioned in the Federal Trade Commission Trade Practice Rules for the Jewelry Industry for identifying a cultured pearl. Inasmuch as the volume of the better tissue-graft cultured pearls is composed of from approximately 75% to nearly 100% nacre, whereas the mother-of-pearl nucleated salt and freshwater pearls are only approximately 5 % to 20% nacre, there appears to be valid reason to differentiate between the two.

It has been suggested that the term "freshwater cultured pearls" be used for them. Possibly, since both nucleated and non-nucleated cultured pearls from freshwater clams are being marketed, the term "tissue-graft cultured fresh-water pearls" describes them best, but is an awkward term. Another suggestion has been that, since Lake Biwa, so far, is the only culturing center for these pearls, the term "Biwa cultured pearls" be used. This suggestion is not valid for the Gem Trade Laboratories, since we do not attempt to give sources of other gem materials.

General agreement on terminology for this new product has not been reached.

Other Problems of Pearl Terminology to be Solved

Problems of terminology are not confined to the relatively new, freshwater cultured pearls. In fact, the very term "cultured pearl" is still questioned by those who claim it does not adequately describe what is being sold. These people would prefer some term such "nacre veneered mother-of-pearl beads." However, since the first term has been accepted, and since more than half of the volume of some of the very large Australian and Burma cultured pearl may be composed of nacre, no single term would seem adequate to describe all nucleated pearls.

There remains the problem of pearls without nuclei recovered from saltwater cultivated-pearl oysters. After removing the pearl or pearls from the oysters, most of the operators remove the bodies from the shells, lightly macerate them, and mix the whole with sea water. From this sediment. are extracted small accidental pearls, as well as accidental baroque pearls, all of which may have started from a variety of causes. In certain cases, it is known that if a nucleus is expelled shortly after the nucleus-insertion operation, the tissue that was inserted may remain, giving the necessary stimulus to form a pearl sac and consequent "accidental tissue-graft cultured pearl."

Such baroque pearls, when X-rayed, give a radiograph pattern precisely like the very baroque tissue-graft pearl pattern of fresh-water cultured pearls. Other baroque pearls taken from this residue may not show a hollow center and when the radiograph is compared with that of natural pearl, they are the same. These solid pearls could have formed as a result of some parasite or other exciting organism or physiological condition while the pearl oyster lay in its cage, or the stimulus could have resulted from loosened epithelial tissue caused by the probing and cutting necessary for the nucleus implantation.

Formerly, the residue pearls were sold for "pearl medicine." Lately, some of them have been offered in the market as natural pearls or "natural rose-bud pearls." In one case, small nearly round, well-matched pearls were brought to the New York Laboratory for examination. Their color was good, but under the microscope they had a flaky appearance. It was our feeling that they had been over-bleached to remove what is commonly a fault of pearls from Pinctada martensii. a tendency to be greenish or yellow. Many of these small pearls showed a pattern in their radiograph that was reminiscent of freshwater tissue-graft cultured pearls.

The Federal Trade Commission Rulings were drawn up before the freshwater cultured pearls or the non-nucleated salt-water pearls were a commercial factor. Therefore, the Laboratories of the Gemological Institute have had to interpret the rulings in the best interests of the buying public, whenever the pearls submitted have been identifiable. In the case of the hollow-center saltwater pearls, their appearance and radiographs serve to indicate their source. Whether or not they were "caused or induced by man" is a moot question.

In the case of solid pearls from the cultivated pearl oysters, only their association in lots or strands with the hollow centered pearls would indicate their source. Alone, they would be identified as natural pearls, since no clues may be had from X-rays, ultraviolet fluorescence or radiographs.

These solid pearls, too, beg the question as to whether or not they were "caused or induced by man." Certainly, in the broad aspect, the gathering either of spat or immature pearl oysters or clams and rearing them in prepared baskets was "caused and induced by man." In this sense, any concretions taken from such pearl oysters or clams would not be natural pearls. However, the FTC definition of a cultured pearl, "The composite product created when a nucleus (usually a sphere of calcareous mollusc shell) planted by man inside the shell or in the mantle of a mollusc is coated with nacre by the mollusc" leaves something to be desired when the matter of non-nucleated salt-water pearls from cultivated pearl oysters is considered. Possibly, the whole matter is only academic, since it is not known if any commercial tissue-graft culturing is being carried out in Pinctada martensii . In view of its relatively short life span and its small size, it is doubtful if such a process could be used successfully.

The matter of freshwater cultured pearl terminology is not academic when we consider that in both Japan and India, export papers describe the product as "natural pearls." Since they reach America from these countries under this description, the official papers carry some weight with importers and brokers who have contested the contraption by the Laboratories. They point out that they go into India duty free as "natural pearls," whereas there is a 25% duty for cultured pearls. We are in agreement that the product deserves a descriptive and marketable term that will serve to distinguish them from ordinary nucleated cultured pearls.

But, just as the production of synthetic rubies, sapphires and emeralds is controlled by man, and hence the factor of rarity, or lack of it, is controlled, one of the prime factors in the value of natural gem materials is lacking, for the production of these objects of beauty IS also controlled by man.

References 1. Alexander, Dr. A. W., NATIONAL ]EWELER, December, 1961.
2. Cahn, Dr. A. R., Pearl Culture in  Bureau of Fisheries leaflet 357, 1948.
3. Kunz, Dr. G. F., The Book of the Pearl, 1908.