Akoya – Ocean-Cultured Pearls

Round, smooth, precisely measured and orderly, akoya pearls have the classic look that many find indispensible with business and formal attire. These ocean pearls, cultivated exclusively in-body in small Pinctada species that live in temperate waters, remained what most people meant by pearls for close to half a century. Japan exported the technology made famous by K. Mikimoto to Australia, making Southsea pearl cultivation using much larger tropical Pinctada species possible. Later, it was also brought to China, where ocean pearl cultivation developed much less rapidly than freshwater cultivation. Read more in detail about provenance. The valuation of akoya pearls is based on degree of perfection and size. The shape is mainly prized for faithful adherence to the perfectly spherical tool-made shell bead nucleus (generally freshwater mussel shell is used, preferably from USA). Perfection is of course elusive, and where natural processes are relied on for production, it is not a reasonable requirement. The degree of perfection desired from akoya pearls can easily be obtained in imitation pearls made with modern machinery. Some manufacturers try, albeit with little success, to add convincing flaws to their simulants. Pearl imitations are easily detected because they have a paint surface, and therefore are rarely a concern for pearl buyers. However, an oversimplification of the concept of quality that disregards nacre thickness has caused the proliferation of akoya pearls with extremely thin coating. These could not satisfy the expectations of many customers, most of whom assumed they were buying durable gems. Read more in detail nacre thickness. Akoya pearls' color is widely expected to be white or white-pink, the least likely to occur naturally in shells that are creamy-yellow to greenish. The most unnatural color that bleaching can acheive without losing too much lustre is valued highest. Relatively light color has long been a priority in breeding pearl oysters, so few are yellow enough to satisfy the recent demand for "golden" color. As a result, previously unimaginable yellow dye came into widespread use nearly a decade ago. Read more in detail about color treatments. A perfectionist approach, based on rejection of many of akoya pearls' natural characteristics, thus defined the popular ideal. It probably pleased jewelers familiar with gemstone grading, and helped cultured pearls gain their place alongside the noble minerals. Giving priority to such factors as flawless surface at any but exalted price points is however misguided. Not only does it encourage consumers to buy a pretense of quality, it causes pretend quality to become the norm. Now under pressure from both China freshwater and southsea competition, akoya pearls have become excellent value for those who approach the product realistically. This requires some understanding of the nature of the product, and of the tradeoffs inherent in each valuation factor. Individual taste does vary, at least in terms of priorities among desired factors. Guided by market knowledge, those preferences should determine pearl choices, especially regarding quality and color. Large pearls tend to have more irregularities, because they need more nacre thickness than small ones do in order to avoid the nucleus showing through. Always inspect pearls by rotating all or most of a strand... this not only shows the irregularities on all sides, but a reflection from within the shell bead nucleus of the pearl (moonstone effect) occurs when the coating is very thin. Such pearls should be excluded from surface quality comparisons because their nacre is too thin to be durable. Read more in detail nacre thickness.


Much of Japan's shrinking pearl cultivation industry has been operating at a loss for many years. Akoya pearl cultivation projects have been underway in China for decades, but progress has been slow compared to that of freshwater pearl cultivation in the mantle. Sizes 7.5mm and below are hardly cultivated in Japan, as China supplies most of the world's requirements for small sizes. Some of these are processed in Japan and come to market as "product of Japan", as do Tahitian and other southsea pearl strands assembled there. Those processed in China and marketed as "made in China" may of course include lower qualities, but are oftentimes better value for money when pearls adequate to the purpose can be found. A leading US importer of akoya pearls announced a few years ago that it was his policy to value akoya pearls strictly on their merits, ie without regard to whether they were grown in Japan or China. We were inclined to agree, as we are no more able than he to tell the difference!

Nacre Thickness

Akoya pearls with adequate to thick nacre coating are a magnificent product which usually retains its beauty through remarkably long use. Such pearls usually have some degree of deviation from the bead nucleus' spherical shape. Slightly ovoid shapes are called semi-round, more irregular ones semi-baroque, and a majority of thick-coated akoya will be quite baroque. The most valuable akoya pearls are those which have been left in long enough to acquire adequate nacre thickness, but have exceptionally few irregularities and surface flaws in spite of it. However, it is far more cost-effective to produce pearls with near-perfect surface by keeping nacre thickness minimal. Of course, such pearls are not as durable, but hardly anyone asks about that. With the introduction of akoya pearls to the mass market, the perfectionist approach affected the durability of pearls produced to disadvantage. Round pearls with good nacre coating could not be produced to match retail price points. No pearl producer wishing to take advantage of the expanded market had any choice but to make pearls with very thin nacre coating, as that saved costs and largely eliminated the occurrence of baroques, for which demand was low. Extremely thin-coated pearls are called "sudare" in the trade in Japan, a reference to chick blinds. When a thin coated pearl with a bead nucleus is rotated, a deep reflection from the nucleus' near-flat nacre layers (moonstone effect) can be seen. 90 degrees from that, the edges of the nucleus layers are sometimes visible as stripes. The simile is between that striping and light filtering through a straw or bamboo chick blind. Many such pearls, after being subjected to strong bleaching, were so weakened that they lost all of their nacre coating, and reverted to bare mother-of-pearl beads. Sometimes nacre can be removed by prying at drill holes with fingernail or penknife - if a hard, brittle layer usually much thinner than an eggshell can be removed, you have transformed what got by as a cultured pearl back into a mother-of-pearl bead. Such beads cannot be re-used for cultivation because they may have absorbed enough peroxide to kill the mollusc if implanted. K. Mikimoto generated a lot of publicity by acquiring a quantity of extremely thin-coated and misprocessed pearls and publicly incinerating them, causing of course a great stench. Rudolf Voll contributed his concerns about the durability of the akoya pearls being exported on a large scale during the 1960's to the English-language press in Japan. For nearly four decades, pearls exported from Japan were required to pass an inspection by fisheries ministry officials, chiefly aimed at ascertaining that the nacre coating was adequate. This determination was made by visual inspection, without reliance on radiography or any device to measure nacre thickness in microns or as a percentage of mass. However, orders continued to insist on round pearls with smooth surface at low prices... and to enable the industry to meet those demands, the unwritten standard of adequacy had to be kept quite low. A decade after the end of the government export inspection, pearl grading companies in Japan offer various kinds of certification for akoya pearls, especially strands. An advertisement from a vendor of strands so certified defines "hanadama" (flower pearls, traditionally the top circa 5% of round akoya pearl strands produced in a year) as a grade by stipulating nacre thickness as 5% of the mass, perhaps calculated by comparing the pearls' weight to that of bare nuclei. An 8.5mm diameter pearl with 5% nacre could be expected to have approx. 0.42mm of nacre on both sides combined, a single nacre thickness of less than 0.22mm... and 95% of akoya with similar nacre thickness are too imperfect for this grade. Most akoya pearls with as much as half a millimeter of nacre thickness are excluded from top grades, because they deviate from the smooth and spherical. It is necessary to make pearl purchasers aware of nacre thickness and its effects on shape, surface, and durability. The preoccupation with round shape and smooth surface is usually learned rather than innate. It has been our experience that, given this knowledge and the opportunity to choose from a variety of akoya pearl qualities (not all round and smooth), people quickly discover an individual set of priorities and preferences. They are much less likely to demand an unreasonable degree of surface smoothness relative to cost, which can only be satisfied with thin-coated pearls.

Color Treatments

Most white pearls have been bleached. It stands to reason that a laboratory should be able to determine whether a pearl contains residues of chemical treatments, but many gem labs do not offer this service. Pearl processing equipment for washing and bleaching has not seen much publicity since then.

Natural pearls had been bleached for centuries before cultivation began, suggesting that aesthetes felt the need even then to improve on nature. The most benign method of bleaching is exposure to sunlight, which is effective in lightening some typical colors of freshwater mussel pearls. This was rediscovered in 1960's Japan after a parcel of freshwater pearls sent to India by Uda Pearl Co was returned. While being reforwarded around India for 2 years in translucent airmail packaging, the peachy-creamy pearls had become brilliantly white. Freshwater pearl processors began modifying ice boxes, which were being discarded in large numbers following the introduction of affordable refrigerators, with light bulbs to simulate the process. This kind of bleaching appears to have little or no detrimental effect on pearl lustre. However ocean pearl color is mostly unaffected by visible or uv light irradiation. Sunlight bleaching of China fw pearls seems to have been largely abandoned during the 1980's in favor of chemical treatments, which are faster and more powerful. Practically all akoya pearls are treated with hydrogen peroxide bleach. This serves two purposes. One is "spot removal", done on all pearls except for some to be dyed dark colors. The vast majority of akoya pearls are harvested with small grey spots that respond well to mild bleaching, which may not significantly alter their color. Until a recent craze for "golden" akoya has led to quite a lot of pearls being dyed yellow, it has been most common to lighten the color in the same operation, by bleaching more intensely, for longer time and/or at higher temperature. The main cost of more bleaching is in the form of more pearls that lose lustre and thus value. Most of this loss occurs during treatment, and some durimg subsequent months and years. In the latter case, dealers are forced to cull pearls from strands, and commonly consumers are told that their use of cosmetics (or constitutional chemsitry) is at fault. Bleaching is usually done after pre-sorting and drilling akoya pearls, and before final sorting into loose pearl lots and strands. Undrilled pearls are slower to bleach because the peroxide must penetrate the nacre, but the drill holes allow it to be absorbed below the nacre. Though preferable to all alternatives, hydrogen peroxide has a solubility problem. Despite the use of modern equipment such as high-speed centrifuges, it is difficult to eliminate the oxidant completely from treated pearls. This helps to explain why highly-bleached akoya pearls tend to change more rapidly than typical creamy colors. The state of the art of pearl processing is a trade secret of each processor, and far from seeking to provide details of color removal treatments, the convention remains nondisclosure. Only treatments obviously adding color, by means of dye or nuclear irradiation, are usually disclosed when pearls are sold.  Cobalt 60-gamma irradiation turns freshwater pearl nacre grey - and affects akoya pearls because their nuclei are freshwater. Ironically, added color is much less likely to impact pearls' durability than bleaching. The addition of blue color was a prerequisite for exporting naturally blue-grey baroque akoya pearls from Japan while the government inspection was required. This was because the natural color is unstable, ie fades and may become spotty, thus dye treatment was considered a necessary improvement. It took many years for golden color, long appreciated in southsea pearls, to become a desired color of akoya pearls.  Since for the preceding half century, akoya shells have been bred largely for their whiteness,  not enough pearls with strong goldy yellow color occur naturally to meet the new demand.   Yet most lots of extremely yellow pearls are marketed as natural color, leading us to believe that nondisclosure is as much the norm with yellow dyeing as it is with bleaching. Color treatments affect the nacre of a pearl, either bleaching or staining it. That nacre coating remains the source of the pearl's lustre after treatment. Paints like nail polish, which cover a pearl's surface, providing lustre from the paint layer, are not pearl treatments. When they are applied to pearls, they transform them into imitation pearls. Similarly, faceting pearls by cutting away their surface transforms them into the equivalent of shell beads.    Most vendors of painted and of faceted ex-pearls call them pearls.  We recommend classifying such material outside the definition of pearls, if indeed it is worthwhile carrying it. There has always been a need to improve the lustre, especially of pearls that lost it to bleaching. Tumbling with bits of bamboo impregnated with silicone and/or all manner of shiny resins and secret ingredients is very common for all types of Chinese pearls. In Japan there was a treatment for akoya pearls with eye-poppingly unnatural results that required the use of ether. It was called bakudan-zome (bomb dye) because of what happens when one is not careful with ether. More recently, there have been occasional announcements of treatments likely to affect pearl lustre, such as polymer coating, never to be heard of again. Successful lustre enhancement treatments can add more value if undisclosed, might actually improve durability, and may remain undetectable for a long time. Uncertainty about this has deterred us from investing heavily in high-cost akoya pearls with extremely unnatural color and/or uncanny lustre. The monochrome image above was sold (including publication rights) by Japan Pearl Export Processing Assn (JPEPA) to its members, including Pacific Pearls, circa 1960. Soon after that it disappeared, and by the time color photos became available, only cultivation and sorting scenes were offered. We surmised that some other member(s) had pointed out that, since by convention pearl bleaching is not disclosed, it would be better not to publish photographs of the equipment used to do it.