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Akoya Pearl Nacre and Luster


For Mastoloni pearl experts, nacre and luster are the most important indicators of quality; however, most people do not understand what nacre is. Nacre is the hard, iridescent coating that oysters (and some other mollusks) use to line the inside of their shells. Nacre is also what pearls are made of.


Nacre consists of different laminated layers of calcium carbonate stuck together with elastic bio-polymers. Nacre's iridescence is caused by 'aragonite,' a calcium carbonate material. These layers of aragonite cause different colors of light to be reflected from different viewing angles.

Nacre density is a result of the formation of aragonite platelets. Platelets in a very loose formation cannot refract and reflect light as well as very tightly packed platelets. The loose formation phenomenon occurs more often in pearls grown in warm water.


Because the average consumer is not able to determine nacre quality, the most important factor for the consumer to understand is luster, which can easily be judged by the naked eye.

Pearls with high luster sharply reflect images around them, like a mirror. They display depth or three-dimensional glow and a subtle display of Orient—different surface colors. Pearls with low luster often look dull, chalky and lifeless.

Luster is the reflection and refraction of light as it passes through layers of aragonite. The intensity of luster is determined not only by the quantity of crystals but also by the specific geometric pattern they are secreted in by the mollusk.

Many outside factors affect nacre secretion, the determining factor of luster. The health of the oyster, the water temperature of the host environment and the level of nutrients available to the oyster all play a vital role in creating a pearl with superior luster.

Though the intensity of a pearl's luster can be an indicator of nacre thickness—and thus the durability of a pearl—this correlation is not always accurate. Some cultured pearls have very thick nacre combined with poor density resulting in mediocre luster.


Chinese Akoya Pearls are cultivated in warm waters during the entire nacre growing period. Warm water promotes quicker nacre coating but the coating is often what experts refer to as 'soft,' or non-durable and typically lacking good luster.

The waters in which Japanese Akoya Pearls are farmed are far less polluted and less subject to changes in water temperature. Cold waters slow down the nacre secretion process by reducing the size of aragonite platelets and producing tighter, more densely packed nacre layers. Japanese producers conduct their harvesting only once a year in the freezing winter weather to ensure that the cold-water pearl coating is at its peak. Temperature combined with minimal pollution gives the fine quality Japanese Akoya Pearls their 'mirror-like' luster.


Given today's market, the answer is yes and no.

Over the past 50 years, the world's weather patterns and economic conditions have changed. Fifteen years ago, the total Japanese domestic pearl crop yielded 70% more than it currently does.

Shifting weather patterns and global ocean pollution affect the health of oysters and hinders their ability to produce fine pearls. Labor costs in Japan, even in the most remote regions, have been steadily rising. Major advances in Chinese pearl production, the termination of the Japanese Pearl Quality Regulatory Agency (JPEA) and other global economic factors have all contributed to the high scarcity of Japanese Akoya Pearls.


Today, the wholesale Japanese pearl houses in Kobe remain the largest source for fine quality Akoya Pearls. These wholesale Japanese pearl houses are extremely selective about their clients and limit access to their products. Only a few companies, Mastoloni included, which have spent generations forging trusted relationships, are offered these pearls. This is why Mastoloni's grading scales are higher than other companies.