Pearl Color Research Articles

Is pearl colour produced fromPinctada margaritiferapredictable through shell phenotypes and rearing environments selections?

The black-lipped pearl oyster, Pinctada margaritifera, is the most important farmed mollusc species in French Polynesia. Donor oyster selection among wild P. margaritifera individuals, chosen according to their inner shell colour, makes it possible to obtain the broadest range of cultured pearl colours of any species. This study demonstrates the relative influence of using black [B] or red [R] outer shell phenotypes, combined with green [G] or yellow [Y] inner shell phenotypes, on pearl darkness level, colour categories and lustre. A large scale grafting experiment was designed and carried out over five grow-out locations, covering three archipelagos: Tuamotus, Society and Gambier. Results revealed that the [B + G] phenotypes may be used as donors to produce dark green pearl, which suit the demands of the Asian market; whereas, phenotypes incorporating [R] and/or [Y] phenotypes may be used to obtain multicolour pearls of medium/light darkness, which suit the demands of the European market. From an environmental point of view, the 1) [B] phenotype showed no significant variation for light and other pearl colour production, and 2) [Y] phenotype produced both the same rate of pearl darkness level and green colour pearls whatever the grow-out location. A classification tree model was built to predict, according to shell phenotype and culture location, the colour and darkness level of harvested pearls. Lustre was shown to be more influenced by the environment than by phenotype. These results should be taken into account in pearl farm production management and in selective breeding programmes.

The Use of Probabilistic Neural Network and UV Reflectance Spectroscopy as an Objective Cultured Pearl Quality Grading Method

Pearl quality and value are determined as a combination of different features, with mollusk species, nacre thickness, luster, surface, shape, color and pearl size, being the most important. A pearl grader has to quantify visual observations and to assign a grading level to a pearl. The aim of this work was to reduce subjectivity in the assessment of some aspects of pearl quality by using artificial neural networks to predict pearl quality parameters from UV reflectance spectra. Given the good predictability of our previous model that used multilayer perceptron ANN modeling of UVVisible spectra to predict the grade of pearls, we wanted to simplify and improve the model by reducing the spectral input to UV only and by using classifier neural network modelling. It is hypothesized that as UV light is of higher energy than visible light, it may penetrate further into the surface of the pearl, and hence the corresponding UV diffuse reflectance spectrum may provide more information that can be used to assess pearl quality. The developed models were successful in predicting mollusk pearl growing species, pearl and donor color, luster, and surface complexity. The simplified models have been built resulting in more accurate prediction of selected pearl quality parameters when compared with the previous reported model.

Quantitative trait loci and genetic association analysis reveals insights into complex pearl quality traits in donor silver-lipped pearl oysters

Abstract Pearl oysters are commercially farmed for their gemstone quality pearls worldwide and are an important animal model for understanding bivalve biology. However, despite their economic and scientific significance, limited quantitative genetic studies have been undertaken to identify genes that regulate important pearl quality traits and unique biological characteristics (i.e. biomineralisation). Over the last decade, pearling industries worldwide have shown strong interest in genetic stock improvement aiming to increase the production of high quality ‘South Sea’ pearls. However, before genetic breeding programmes can be initiated, the genetic architecture of such traits needs to be elucidated. This study investigates the genetic architecture of complex pearl quality traits (pearl size, weight, surface complexion and colour) and presents the first putative quantitative trait loci (QTL) and genetic associations to these commercially important pearl quality traits. To identify QTL and genetic associations to pearl quality traits, a total of 2114 pearl grading records were recorded over 342 pearl oysters. Utilising these phenotypic records, this study provides strong evidence that pearl quality traits have a low to moderate additive genetic component ( h 2 from 0.14 to 0.34) and supports previous quantitative genetic studies that these traits are polygenic in nature. A total of nine putative QTL and 25 marker associations for pearl colour, one QTL for pearl surface complexion and three genetic associations to pearl size and weight were identified using 11 half-sib families. The majority of QTL and genetic associations were detected for pearl colour whereby the most prominent QTL were located within a 2 cM interval on LG10. QTL in this region were mapped for four out of five sub-categories of pearl colour and explained from 32% to 46.1% of the phenotypic variation observed in pearl colour. Segregation in multiple families provides further support that genes localised to this region have significant effects on pearl colour. The segregation of these preliminary QTL and detection of genetic associations provide insights into the genetic architecture of pearl quality traits and will direct further research into the establishment of genetic breeding programmes for pearl quality within the Pinctada maxima pearling industry.

Influence of nacre deposition rate on cultured pearl grade and colour in the black-lipped pearl oyster Pinctada margaritifera using farmed donor families

Cultured pearl nacre deposition rate in Pinctada margaritifera oysters was studied to examine its influence on Tahitian classification grade and colour and to further our understanding of using selected donor oysters produced in a hatchery system for the improvement of these traits. A large-scale grafting experiment using 150 farmed donor oysters was realised in Rangiroa atoll (French Polynesia). After 18 months of culture, 874 pearls were harvested and 7 pearls quality traits were recorded: (1) nacre deposition rate assessed by nacre thickness and weight, (2) classification grade, lustre and surface defects, and (3) colour assessed by pearl colour darkness level and visual colour categories. Nacre deposition rate significantly influence pearl grade, surface defects, darkness level and colour categories, but not the lustre. Grade A pearls had the thickest and heaviest nacre on average, compared with grade D pearls and rejects. In addition, pearls without any surface defect had thicker and heavier nacre. Pearls with low darkness were the thinnest and the lightest. Pearls of aubergine–peacock secondary colours were the thickest and the heaviest. These results highlight the importance of rapid nacre deposition rate for increasing the production of grade A pearls, with less surface defects and dominance of a black tone colour. Fast nacre deposition may, however, have a negative impact on other pearl quality traits, such as pearl lustre. This study demonstrates the importance of examining relationships between pearl quality traits in a way that provides solid information that can be directly used for breeding and genetic selection programmes.

Influence of Astaxanthin on Pearl Oyster <i>Pinctada martensii</i>

In the study, through the addition astaxanthin into the bait for the pearl oyster Pinctada martensii for 3 months, we studied the accumulation and existence form of astaxanthin in pearl oyster through qualitative and quantitative analysis which adopted High Performance Liquid Chromatography method; the transmission of astaxanthin in shells was detected by Micro-Raman spectrometry. The results showed: 6.870±1.356μg/g of astaxanthin existed in the control group of Pinctada martensii, and 74.799±5.907μg/g of astaxanthin existed in the experimental group, some of them were existent in the form of astaxanthin esters. Weak carotenoid characteristic peak occurred in the control group, while the carotenoid characteristic peaks intensity enhanced obviously in the experimental group, which illustrated remarkable increase of carotenoid content in the shell. These findings will not only provide the basis for colorful pearl cultivation via food-borne transmission but also lay a foundation for further artificial regulation and control of pearl color.

Family effect on cultured pearl quality in black-lipped pearl oysterPinctada margaritiferaand insights for genetic improvement

Individual Pinctada margaritifera molluscs were collected from the Takapoto atoll (Tuamotu Archipelago, French Polynesia) and used to produce ten first generation full-sib families in a hatchery system, following artificial breeding protocols. After three years of culture, these progenies were transferred to Rangiroa atoll (Tuamotu Archipelago, French Polynesia) and tested for their potential as graft donors. A large-scale grafting experiment of 1500 grafts was conducted, in which a single professional grafter used ten individual donor oysters from each of the ten families, grafting 15 recipient oysters from each donor. The recipient oysters were all obtained from wild spat collection in Ahe (Tuamotu Archipelago, French Polynesia). After 18 months of culture, 874 pearls were harvested. Highly significant donor family effects were found for nucleus retention, nacre thickness, nacre weight, pearl colour darkness and visually-perceived colour (bodycolor and overtone), pearl shape categories, surface defects and lustre, the last two of which are components of the Tahitian classification grade. No significant difference was recorded between the ten G1 families for the absence or presence of rings. The progenies could be ranked from “best” (i.e., the donor whose grafts produced the greatest number of grade A pearls) to the “worst”. Some progenies had extreme characteristics: family B presented the greatest number of pearls with lustre (98%) and a high proportion of dark gray to black with green overtone pearls (70%). These results have important implications for the selective breeding of donor pearl oysters: it may be possible to reach a point where specific donor lines whose grafts produce pearls with specific quality traits could be identified and maintained as specific breeding lines.

Evaluation of the susceptibility to pigmentation of orthodontic esthetic elastomeric ligatures

The purpose of this laboratory study was to evaluate changes in the pigmentation of esthetic elastomeric ligatures after immersion in a staining solution. Sixty ligatures were selected and divided into 12 groups according to their brand and also considering their condition, i.e., unstretched or stretched. The groups were divided into: Morelli (clear), TP Orthodontics (clear), American Orthodontics (clear), 3M/Unitek (clear), American Orthodontics (pearl color) and 3M/Unitek (pearl color), separated in groups of 5 unstretched and 5 stretched ligatures. Assessment of their color changes was performed by means of digital photograph and computer analysis using Adobe Photoshop. Standardized digital photographs were taken at T₀ (before the staining process, with unstretched ligatures) and at T₁ (following the 5-days staining process). The staining solution was composed of artificial saliva and foods with staining potential. At T₁ the ligatures were either stretched or unstretched. The results of this study showed that esthetic elastomeric ligatures are prone to staining. Among the evaluated brands, TP Orthodontics and American Orthodontics clear ligatures were the most stable. Moreover, 3M/Unitek pearl ligatures demonstrated statistically significant changes in all variables. Esthetic elastomeric ligatures are susceptible to staining and no statistically significant difference was found between unstretched or stretched ligatures, with the sole exception of the TP Orthodontics brand. The 3M/Unitek's pearl color ligatures displayed the greatest staining potential.

Contribution of donor and host oysters to the cultured pearl colour inPinctada martensii

Cultured free round pearls are produced by implanting a spherical nucleus with a small piece of nacre-secreting mantle graft from a donor oyster into the gonad of a recipient oyster (host). To examine the possible contribution of host and donor oysters to the colouration of the harvested pearls, the CSE-1 Imaging and Color-Measuring System were used to quantitatively measure the L*a*b* values of donor and host shells and the produced pearls in Pinctada martensii. Results showed that the colour of pearls had significant positive correlation (r = 0.1–0.22, P = 0.00) with that of donors, but had no correlation with that of host oysters, thus convincingly confirmed the contribution of nacre colour of donor to the realization of pearl quality of colour. To further clarify the relationship between the donor and the pearl colour, the donors from pearls of good and poor colour quality were further compared and the results demonstrated the significant difference in L* values (P < 0.05) and insignificant difference in a* and b* values, suggesting the necessity of selecting donors with bright and lustrous nacre in pearl production.

The Use of UV-Visible Reflectance Spectroscopy as an Objective Tool to Evaluate Pearl Quality

Assessing the quality of pearls involves the use of various tools and methods, which are mainly visual and often quite subjective. Pearls are normally classified by origin and are then graded by luster, nacre thickness, surface quality, size, color and shape. The aim of this study was to investigate the capacity of Artificial Neural Networks (ANNs) to classify and estimate the quality of 27 different pearls from their UV-Visible spectra. Due to the opaque nature of pearls, spectroscopy measurements were performed using the Diffuse Reflectance UV-Visible spectroscopy technique. The spectra were acquired at two different locations on each pearl sample in order to assess surface homogeneity. The spectral data (inputs) were smoothed to reduce the noise, fed into ANNs and correlated to the pearl’s quality/grading criteria (outputs). The developed ANNs were successful in predicting pearl type, mollusk growing species, possible luster and color enhancing, donor condition/type, recipient/host color, donor color, pearl luster, pearl color, origin. The results of this study shows that the developed UV-Vis spectroscopy-ANN method could be used as a more objective method of assessing pearl quality (grading) and may become a valuable tool for the pearl grading industry.

Evidence of donor effect on cultured pearl quality from a duplicated grafting experiment onPinctada margaritiferausing wild donors

Producing high quality cultured black pearls from Pinctada margaritifera is one of the major challenges for the oyster industry in French Polynesia. In order to assess donor effect on cultured pearl quality, wild Pinctada margaritifera originating from the Tuamotu Archipelago were used in a duplicated grafting experiment. After 12 months of culture, nucleus retention was assessed and seven pearl quality traits recorded on the 454 cultured pearls harvested from the experiment. The traits scored were nacre thickness and pearl weight, surface defects, lustre, grade, and the components: 1) darkness of cultured pearl colour, and 2) visual perception of class (bodycolor and/or overtone). Our results demonstrate for the first time that individual wild donors of implanted mantle grafts significantly affect these seven quality traits in P. margaritifera cultured pearls. This finding was repeated in two series of grafts made by different professional grafters. The wild donors could be ranked from best (e.g., the donor whose grafts produced the cultured pearl with the maximum lustre) to the worst. Moreover, we showed strong correlations between: 1) cultured pearl nacre thickness and grade, with grade A showing the greatest nacre thickness on average compared with grade D and rejects; and 2) nacre thickness/cultured pearl weight and components (darkness and visual colour categories), with the palest cultured pearls (i.e. white cultured pearls) being the smallest (lowest nacre thickness and weight). Thus, one way of enhancing P. margaritifera foundation stocks for a selective breeding program could be to select the best donors, using appropriate molecular tools. Generation of selected donor lines from these stocks through hatchery production would be one way to increase the quality of cultured pearl farming of P. margaritifera in French Polynesia.

Effects of dietary Europium complex and Europium(III) on cultured pearl colour in the pearl oysterPinctada martensii

In the present study, through a transmission experiment, the effects of europium complex and Eu3+ on the pearl colour in the pearl oyster Pinctada martensii were evaluated. Europium complex and europium salt were respectively enriched by dietary green algae platymonas subcordiformi, and their toxicity to algae were analysed by the 96-h acute toxic experiment. Then, the green algae enriched europium complex and europium salt were respectively fed pearl oysters for 2 months, and the surface microstructures of cultured pearls were presented with scanning electron microscopy (SEM) and atomic force microscope(AFM). The results show that toxicity of europium complex to algae is much lower than Eu3+ from lowest no observable effect concentration LNOEC values and 96h-EC50 values and two compounds can modify pearl structure and optimize pearl colour from SEM and AFM images. Taken together, our results, for the first time, show that rare earth complex can improve the pearl quality. This study provides an innovative approach for additional investigation of the influence of rare earth elements on pearls.

Identification of Irradiated South Sea Cultured Pearls Using Electron Spin Resonance Spectroscopy

GEMS & GEMOLOGY WINTER 2012 I dyeing, bleaching, and heat treatment are widely used methods to alter pearl color. Although most artificial colors are easily recognized, some resemble attractive colors that occur in nature (Elen, 2001; Li and Chen, 2001; Zachovay, 2005; Wang et al., 2006; “Better techniques improve brown pearls,” 2006; McClure et al., 2010). Lower-quality freshwater and saltwater cultured pearls are regularly exposed to 60Co gamma-ray radiation in an attempt to simulate black pearls or enhance orient (Crowningshield, 1988; Li and Chen, 2002; O’Donoghue, 2006). In recent years, the irradiation process has been applied to not only Akoya cultured pearls and freshwater cultured pearls (FWCPs), but also to South Sea cultured pearls (SSCPs) (Choi et al., 2012). The irradiation-induced color change results from the darkening of the nucleus, caused by MnCO3 oxidation, as well as denatured damage to the pearl’s conchiolin (Matsuda and Miyoshi, 1988). FWCPs have a higher abundance of proteinous components and manganese than saltwater pearls (Hatano and Ganno, 1962). Gamma-ray irradiated SSCPs (figure 1) were first discovered in the Korean market in April 2011. At the March 2011 Hong Kong Jewelry Show, a Japanese trader reportedly sold a Korean counterpart irradiated SSCPs without disclosing the treatment. They were light gray or silver loose cultured pearls and beads 10–16 mm in size. While a cream, yellow, or black color is produced by a protein pigment in the nacre, a blue or silver color is caused by organic material between the nacre and nucleus (Komatsu, 1999; O’IDENTIFICATION OF IRRADIATED SOUTH SEA CULTURED PEARLS USING ELECTRON SPIN RESONANCE SPECTROSCOPY

Xenografts and pearl production in two pearl oyster species, P. maxima and P. margaritifera: Effect on pearl quality and a key to understanding genetic contribution

Mantle xenografts between two Pinctada pearl oyster species, P. maxima (silver-lip pearl oyster) and P. margaritifera (black-lip pearl oyster), were used to examine their influence on pearl quality and to further our understanding of the respective contribution host and donor oysters have in pearl formation. Here, host oysters were implanted with mantle tissue originating from either the same species (allograft) or the other species (xenograft) and pearl formation allowed to proceed for 14 months, where after pearls were harvested and nuclei retention and pearl quality traits (nacre deposition/weight, shape, colour, complexion and lustre) recorded. Results showed that xenografts did not significantly affect pearl sac formation and subsequent nuclei retention ( χ 2 = 5.64, df = 3, P > 0.05), but did influence pearl colour, complexion, shape, nacre deposition and nacre weight ( P < 0.05). Nacre deposition and weight were found to be higher in xenografts comprising of a P. maxima donor and P. margaritifera host, than in the reciprocal xenograft and allografts. Pearl colour and complexion were also strongly influenced by the donor oyster species used as xenografts, with P. maxima host oysters implanted with mantle from P. margaritifera producing generally black colour based pearls. Conversely, P. margaritifera hosts implanted with P. maxima mantle produced silver colour based pearls. This study demonstrates the potential of xenografts as a means to improve pearl quality traits such as pearl size, and highlights the role that donor oysters have in the realisation of pearl growth, colour and surface complexion.

The relationship between nacreous layer color and CaCO3 crystal orientation

The pearl or nacreous layer of mollusk shell is composed of CaCO3 aragonite crystals. The factors affecting their color are very complex, such as metal elements, chromoprotein, and nucleation materials, we analyzed the crystal orientation of nacreous layers with different color prepared from fresh water clamsHyriopsis cumingii Lea by X-ray diffraction. The results show that the crystal CaCO3 orientation on specific plane is responsible for the color of pearl and nacreous pearl color.

Color and weight of pearls produced by grafting the mantle tissue from a selected population for white shell color of the Japanese pearl oyster Pinctada fucata martensii (Dunker)

Pearl color and weight were investigated by transplanting mantle tissue from specimens selected for white shell color in the prismatic layer in order to obtain information for selective breeding of the Japanese pearl oyster Pinctada fucata martensii. The frequency of yellow pearls was significantly lower in the group produced by grafting mantle tissue from the inbred white line than from brown lines in two experiments. Pearl weight did not differ between the two groups produced by grafting mantle tissue of white or brown types of donor. Positive correlation was observed between the weight of pearls and that of the shell of host oysters. These results have implications for the selective breeding of host and donor pearl oysters.

ニューラルネットの感度特性を用いた要因特定法と真珠色彩識別への応用

This paper proposes a new method for extracting the sensibility (kansei) of human experts, and applies it to the design of a pearl color evaluation system. A factors identification method using sensitivity of layered neural networks finds the influential factors as the input units which have the greatest influence on all outputs. This method has been applied to the network mapping between spectral reflectance of pearls and the pearl color categories evaluated by experts, and allowed some specific wavelength bands to be identified as the essential factors contributing to the evaluation. Based on this result, a pearl color evaluation system has been designed using multi-bands images (MBI) acquired by combining a monochrome CCD camera with several interference filters corresponding to the identified major wavelength bands factors. Moreover, the identification method has been applied to find the influential factors of each image of MBI and finally the experimental results of discrimination using those factors show that this system is able to give evaluations of pearl color successfully as an expert does.

熱エネルギーと高分子 自動車塗装工程の省エネルギー ホワイト系パール塗色の工程短縮

熱エネルギーと高分子 自動車塗装工程の省エネルギー ホワイト系パール塗色の工程短縮

Trichromatic characterization of the “black pearls” from aquaculture centers of French Polynesia

In the pearl production centers of French Polynesia, which are specialized in “black pearl” production, a statistical shift in pearl color has been noted, possibly resulting from exchanges between populations of the pearl oyster Pinctada margaritifera. Spectral analyses were carried out on pearls covering the whole spectrum of currently observed colors. This paper presents a simplified method making possible a control of the pearl oyster farming and a regulation of pearl production.

HOW TO PREDICT THE SEX OF THE UNBORN INFANT

A fascinating book, entitled The Ladies Dictionary, was published in 1694 in London. The author, who identified himself only by the initials N. H., stated in his preface that he wrote the book "for the use of the Fair-Sex to serve them as a Secret Oracle to consult in all difficult cases." The book is filled with advice and "information" about many intimate topics which women of that period would have probably been too embarrassed to have asked their husbands or physicians. Many answers to questions that N. H. felt women of that period would have wished to have asked the "Learned Men" are fallacious. The following is an excellent example of the untruths offered to the readers of this book: We come now to a nicer Point which we should be difficulty brought to undertake were we not warranted by divers Learned Men who have given their Opinions about it. They tell as if it be a Male Child, that when it is come to some Perfection in the Womb, the Right-Eye of the mother would to appearance move swifter and sparkle more than the other. The Right Pap [breast] rise and swell more than the left, and become harder, the Niple [sic] sooner changing Colour, and the increase of the Milk be more speedy, and being milked out and set in the Sun, it will settle to a Pearl Colour. Her right cheek will often glow and colour more than the other, and she a livelier Blush on all Occasions, than at another time, and is more brisk and free from sadness than if she conceiv'd a Female.