Gauthier, Jean-Pierre
[Centre de Recherches Gemmologiques, Laboratoire de Planétologie et Géodynamique]
Fereire, Jacques
[Centre de Recherches Gemmologiques, Laboratoire de Planétologie et Géodynamique]
Bui, Thanh Nhan
[UCL]
The name Ming pearls refers to gonad-grown Chinese freshwater cultured pearls. In these beaded cultured pearls, the nuclei are predrilled and a tissue graft is placed into the drill hole at the same time the bead is inserted into the mollusc. A large number of these cultured pearls exhibit circling on their surface, typically with one or two main rings and sometimes additional ones. Examination of sliced samples by optical microscopy highlights the primary origin of the circling and the predominant role of predrilling the nucleus. As the cultured pearl rotates during its formation, each orifice on the drilled bead induces a groove on its surface with a spot defect right over the opening. When this drill hole is perpendicular to the rotational axis of the cultured pearl, only one 'equatorial' ring is generated. When there is a fairly large tilt angle between the bead's drill hole and the rotational axis, two grooves appear symmetrically relative to the equatorial plane, diametrically opposite with respect to the nucleus centre. With only a slight tilt angle between the drill hole and the rotational axis, the circles nearly overlap and a narrow ridge might eventually develop between the grooves. The disturbance created by the drill hole is generally more pronounced on the side where the graft was inserted. Round-, drop- and baroque-shaped non-circled Ming cultured pearls were also investigated to clearly understand the influence of the nucleus drill hole. This research raises awareness of one of the major causes of defects that result from grafting techniques using drilled nuclei.
Bibliographic reference |
Gauthier, Jean-Pierre ; Fereire, Jacques ; Bui, Thanh Nhan. An explanation of a specific type of circling as observed on ming cultured pearls. In: The Journal of Gemmology, Vol. 36, no.3, p. 240-252 (2018) |
Permanent URL |
http://hdl.handle.net/2078.1/228763 |