Evidence of Rotation in Flame-Structure Pearls from Bivalves of the Tridacnidae Family

Gauthier, Jean-Pierre; Fereire, Jacques; Bui, Thanh Nhan

doi:10.5741/gems.55.2.216

Cited by 3 publications

(3 citation statements)

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“…The resolution of OCT images along the transverse direction was different from that along the vertical direction because the latter resolution was depended on the refractive index of the medium, resulting in a difference in the voxel size between the transverse and vertical axis [33]. Zeng [34] used an Abbe refractometer to measure the refractive index of pearls, and obtained a typical value of 1.53; Gauthier et al [35] used a jewelry refractometer to measure the refractive index of pearls. Since surface of pearl object was not flat, the far-sighting method was for estimating the refractive index of pearls; Ju et al [15], [16] sliced pearls and calculated their average refractive index of 1.53 by calculating the optical and physical thickness of the slice.…”

Section: Roundness Evaluationmentioning

confidence: 99%

An Automated Grading Method of Pearl Roundness based on Optical Coherence Tomography

Chen,

Zhou,

Yan

et al. 2023

IEEE Photonics J.

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Pearl roundness is an important index in the pearl value evaluation and classification. The existing roundness classification schemes are usually based on 2D image or mechanical methods. However, the 2D image ignores the depth or 3D information, which leads to low classification accuracy, and mechanical classification is easy to cause surface damage. An automated grading method of pearl roundness based on optical coherence tomography is proposed. Based on the high-resolution and low-cost 3D imaging of the pearl surface, through noise reduction, binarization, segmentation, 3D reconstruction, surface extraction, and the surface of pearl is fitted as sphere. A new digital rating index named global local roundness fraction is designed for roundness evaluation, based on the length of the three axes and of coordinates of the fitted sphere. Four grades of pearls were automatically classified by our method, and the results showed that the accuracy of the proposed scheme reached 95%, indicating that the proposed method can be used as an effective means of automatic classification of pearl roundness.

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Section: Roundness Evaluationmentioning

confidence: 99%

An Automated Grading Method of Pearl Roundness based on Optical Coherence Tomography

Chen,

Zhou,

Yan

et al. 2023

IEEE Photonics J.

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“…About the cell distortions. To show that the distortion observed in the lepisphere lattice image depends on the tilt of its normal with respect to the electron beam, we photographed the cross section of a square fiber optic network cable (Gauthier et al, 2017). The first picture was taken with the electron beam normal to the sample (Fig.…”

Section: Spotmentioning

confidence: 99%

Aluminium diboride-type structure in Ethiopian opal-CT revealed by fast Fourier transform

et al. 2018

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Invisible on a scanning electron microscope image of the surface of an Ethiopian opal rough fracture, a periodic arrangement was detected by fast Fourier transform. Using a mask to eliminate the continuous background and keeping only the bright spots in the reciprocal space (fast Fourier transform pattern), an image reconstructed by inverse fast Fourier transform (IFFT) emphasizes a very regular bidisperse array. Taken on a vicinal plane, the image of the successive steps of the stacking allows identification of the crystallographic structure and estimation of the parameters of this aluminium diboride‐type photonic crystal. In addition, another more complex IFFT image allowed confirmation of the structure and determination of the crystallographic indexing of the steps, despite image deformation due to the tilt of the vicinal plane under the electron beam.

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“…Les plus connues et très appréciées en haute joaillerie sont les perles roses de Aliger gigas (Strombus gigas)(Linné, 1758),pink conch ou Queen conch en anglais - (Fritsch & Misiorowski, 1987;Federman & Bari, 2007), suivies par les perles de Melo (Broderip, 1826 pour le genre, Lightfood, 1786 pour l'espèce), moins fréquentes. Rarissimes sont celles d'autres mollusques univalves ou bivalves (voir Gauthier et al 2019).…”

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La coquille flammée du casque rouge, Cypraecassis rufa

Gauthier,

Ferreire,

Bui

2023

Gemmes

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The flame structure of the red helmet shell, Cypraecassis rufa (Linnaeus, 1758) Among molluscs with so-called “porcelaneous” shells, consisting of non-nacreous aragonite, we chose a gastropod, Cypraecassis rufa, to show an example of flame structure on cabochon-cut samples. The crossed structure of this shell, formed of lamellae of different orders, is present in its body. On fragments with a polished flat surface, a moiré effect can be seen. Moreover, on the curved surfaces of the cabochons, a kind of pseudo-chatoyancy appears. The flames are due to the reflection of light on second-order lamellae stacked in first-order lamellae of alternating orientation around their stacking axis.

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Evidence of Rotation in Flame-Structure Pearls from Bivalves of the Tridacnidae Family

Cited by 3 publications

References 0 publications

An Automated Grading Method of Pearl Roundness based on Optical Coherence Tomography

An Automated Grading Method of Pearl Roundness based on Optical Coherence Tomography

Aluminium diboride-type structure in Ethiopian opal-CT revealed by fast Fourier transform

La coquille flammée du casque rouge, Cypraecassis rufa

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