Baroque Pearls Wholesale to Round Pearl : All About Pearls Grading
Pearl quality factors on round pearls to baroque pearls wholesale
Pearls are graded using at least six main quality factors: shape, lustre, surface contour, colour, size and nacre thickness (Matlins, 2002; Strack, 2006; Taylor & Strack, 2008). The relative importance of each depends mainly on the jeweller or pearl producer. However, nowadays all pearls are initially sorted on the basis of species origin before running through these quality factors (J. Shepherd, pers. comm., 2007); for example, South Sea pearls are from Pinctada maxima. This factor however is sometimes difficult to assess unless the pearl grader knows where the pearls were produced. It is even more difficult for the buyers or customers to distinguish the difference and this issue may be open for deception. (source: Baroque Pearls Wholesale)
Lustre on round pearls to baroque pearls wholesale
Fig.1.7. Different types of pearl lustre of South Sea pearls from high (left) to low quality (right). Images supplied by The Autore Group. (source: Baroque Pearls Wholesale)
Lustre describes the reflectance of light from the pearl surface. High lustre means high reflectivity (mirror-like reflectivity) but pearls with low lustre appear chalky or dull (Fig. 1.7). Lustre is probably the major consideration when assessing pearl quality. People tend to buy shining baroque pearls rather than chalky round pearls (Matlins, 2002). However, grading pearls based primarily on this criterion is subjective and open to wide-interpretation (Strack, 2006) due to differences in people’s perception. (source: Baroque Pearls Wholesale)
Shape on round pearls to baroque pearls wholesale
(source: Baroque Pearls Wholesale)
Pearl shapes range from round to baroque (Fig. 1.8). The nucleus is one factor that influences the shape of the pearl. Without a nucleus, pearl shape is usually irregularly (baroque) and to create a round pearl a round nucleus is required as a basis for pearl formation although this does not always result in the formation of round pearls. On this basis, round pearls are more marketable due to their rareness (Matlins, 2002). (source: Baroque Pearls Wholesale)
(source: Baroque Pearls Wholesale)
The shape matrix for pearl grading is divided in three main categories: spherical, symmetrical and baroque (Matlins, 2002; Strack, 2006). The round category is divided in ‘round’ and ‘nearly round’, ‘symmetrical in oval’, ‘button’ and ‘drop’ while baroque is divided into ‘semi baroque’ and ‘baroque’ (Strack, 2006) (Fig. 1.8). In grading South Sea pearls however, a circle shape is also added into the symmetrical category (Fig. 1.8). Tahitian pearls, for example, have a high proportion of ‘circles’ (concentric grooves in the surface of the pearls) (Matlins, 2002). The new pearl shapes on the market today which are based on various nuclei forms: coin pearls, bar pearls (Matlins, 2002) are excluded from this grading matrix which is only applied to round nucleus cultured pearls. (source: Baroque Pearls Wholesale)
Surface complexity on round pearls to baroque pearls wholesale
(source: Baroque Pearls Wholesale)
‘Surface complexity’ assesses the degree of blemishes or flaws covering the surface of a pearl. Blemishes may range from small spots to big chips or cracks or calcareous bumps on the pearl surface (Matlins, 2002). Generally, the fewer surface blemishes a pearl has then the higher its quality. Some types of cultured pearls have a high proportion of surface blemishes. However, in grading South Sea pearls, big ridges forming rings (usually more than three rings) in a pearl is categorised as a circled pearl (Fig. 1.8). Small spots (non calcareous) on the surface of a pearl are usually removed by polishing treatment after harvest. (source: Baroque Pearls Wholesale)
Colour on round pearls to baroque pearls wholesale
(source: Baroque Pearls Wholesale)
Colours of pearls do not merely result from pigments but also from reflection and refraction (Dakin, 1913; Snow et al., 2004), and the nature of the material surrounding the nucleus (Simkiss & Wada, 1980). Thus, pearl structure is an important influence on pearl colour. The phenomenon of iridescence that shows glittering of various colours in a pearl is due to the interference and diffraction of light interacting with the specific structure of a pearl’s surface (Taylor & Strack, 2008)(Fig. 1.10). Iridescence is usually considered with lustre in pearl grading. Another colour phenomenon is overtone or glow. Overtone is a translucent colour that may sometimes appear on pearls together with its original (body) colour (Strack, 2006). However, it may alter the body colour somewhat (Matlins, 2002). A pearl can be named silver-rose, which indicates that silver is the main colour and rose is the overtone (Fig. 1.11). Snow et al. (2004) studied colour in pearls from Pinctada maxima and found that ‘edge-band structure width’ (thickness of the organic matrix) controls the diffraction of lights which consequently create different colour tones; the ticker the edge-band width, the darker the colour, while the more irregular the band, the colour becomes more unsaturated. The main natural pearl colours for pearls produced by P. maxima are shown in Fig. 1.11. (source: Baroque Pearls Wholesale)
Size on round pearls to baroque pearls wholesale
The size of pearls is usually measured in millimetres (mm). Generally, cultured pearls with size below 7 mm are categorised as small pearls, large pearls are above 7 mm (Strack, 2006). However, each type of pearl has its own categorization because larger species of pearl oysters have the capacity to produce larger pearls (Table 1.2). Large Akoya pearls from P. fucata, for example, are more than 7 mm while large South Sea pearls can be up to 20 mm. Large pearls are usually more valuable than the small pearls. (source: Baroque Pearls Wholesale)
(source: Baroque Pearls Wholesale)
Nacre thickness on round pearls to baroque pearls wholesale
The thickness of the nacre layers laid down on the nucleus is measured in millimetres (mm). This factor is applied mainly to cultured pearls. Nacre thickness is strongly related to the length of culture time after the implantation; the longer the culture time the thicker the nacre. In Akoya pearls, nacre thickness below 0.15 mm is categorised as very thin while more than 0.5 mm is very thick (Matlins, 2002; Strack, 2006). South Sea cultured pearls generally have thicker nacre than other pearls and the proportion of nacre is up to 40 to 50% (Matlins, 2002). The minimum thickness of nacre for exported Tahitian pearls is 0.8 mm (Southgate et al., 2008b). Historically, nacre thickness in pearls from P. maxima ranged from 1.5 mm to 5 mm with an average thickness of 2 – 4 mm (Strack, 2006). However, recent years have seen a decline in the nacre thickness of South Sea pearls, particularly those produced in Indonesia (Strack, 2006). (source: Baroque Pearls Wholesale)
Pearl grading systems on round pearls to baroque pearls wholesale
(source: Baroque Pearls Wholesale)
There is no universally accepted system for pearl grading (Matlins, 2002; Strack, 2006). There are currently two systems available for pearl grading: AAA-A and A-D systems. However, both of these are open to interpretation among pearl producers (Matlins, 2002); in some occasions one producer categorize a pearl as AAA grade (following the AAA-A system) while others categorize it as AA grade (Matlins, pers.comm., 2008). These systems have also never been published for scientific use and a system that could be used routinely in grading pearls produces using different experimental procedures is desperately needed. Initially, the AAA-A system was commonly applied to Akoya pearls but it could also be applied for pearls from other species. The system consists of three levels of grading i.e, AAA is the highest, AA is medium and A is the lowest quality pearls for jewellery purposes. Any characteristics below A grade is categorized as a reject pearl. On the other hand, The A-D system has mainly been applied to grading South Sea pearls. The system consists of four grading levels: A is the highest, B is medium-high, C is medium and D is the lowest. Any characteristics below D grade is categorized as a reject pearl. (source: Baroque Pearls Wholesale)
(source: Baroque Pearls Wholesale)
The need for a universal grading system is urgent. Such grading is available for other gemstones such as diamonds. Such a system could be used with natural and cultured pearls and more importantly for the various types of cultured pearls that are common on the market. One potential problem relates to the thickness of the nacre layer of cultured pearls. The market is overwhelmed with pearls which have very thin nacre that is easy to peel off (Matlins, pers.comm., 2007). This result from a short culture time between implantation and pearl harvest and the resulting pearls have a lower price. The system could require a certain minimum nacre thickness, which would influence pearl culture practices. (source: Baroque Pearls Wholesale)
Pearl testing on round pearls to baroque pearls wholesale
(source: Baroque Pearls Wholesale)
Assessing the quality of pearls involves various tools and methods. As summarized by Kennedy (1998), Strack (2006) and Webster (1994), pearl quality tests are mainly visual and often subjective. They involve the use of optical microscopes to differentiate between genuine and fake pearls. Genuine pearls can be recognised by relief lines on their surface under 20 x magnifications while a fake pearls look smooth (Strack, 2006). Natural and cultured pearls can be distinguished using a hole drilled into the pearl. Through this hole the borderline between the nucleus and the nacre can be viewed in cultured pearls. However, for pearls without holes methods using a lucidoscope or endoscope can be applied. These two apparatus need strong light gleaming through the pearls. (source: Baroque Pearls Wholesale)
These methods can also be used to measure the thickness of the nacre. Further methods are X-ray diffraction (lauegram method), X-radiography (skiagram method) and X-ray fluorescence. The last two methods can be applied to determine the thickness of nacre while the former is used for observing the diffraction pattern of the tested pearls. UV-Vis spectrophotometry has been used to distinguish between treated and untreated pearls (Elen, 2001) and to determine characteristic absorption/reflectance spectra that enables identification of species-origin of cultured pearls (Elen, 2002). In conclusion, various tools are used for pearl testing but there is no single method that can be used for overall pearl grading. (source: Baroque Pearls Wholesale)
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