2026

Cultured South Sea pearls with small beads

By Dr. Michael S. Krzemnicki, first published in Facette 30 (March 2026)
Identifying beaded cultured pearls is usually quite straightforward, as such pearls often contain a large bead made from a freshwater shell with a nacre layer only 1.5 mm or less thick. This identification is normally carried out using X-ray methods (radiography and X-ray luminescence), but an experienced gemmologist may sometimes be able to identify a beaded cultured pearl by carefully checking the internal structure of the drill hole in a drilled pearl.
Figure 1: A beaded cultured pearl of 28 ct whose radiography reveals only weak bead-related structures, while a tomographical section clearly shows the spherical bead at the centre of the pearl. Photos: SSEF.

However, it is distinctly more difficult when, during the cultivation process, a very thick (several millimetres) nacre layer is deposited on a small spherical bead. In such cases, it can be challenging to recognise the small bead within the large cultured pearl in radiographic micrographs, particularly if further structures (e.g. drying fissures) in the nacre layer obscure the bead outline in the radiography. Additionally, the slight but characteristic difference in X-ray absorbance between the freshwater bead (which is slightly more absorbing and thus usually brighter) and the surrounding saltwater nacre (which is slightly less absorbing and thus slightly darker grey) may be hidden by the large, thick nacre layer on the small, spherical bead.

X-ray microtomography is very helpful in identifying such beaded cultured pearls in difficult cases (see also Krzemnicki et al., 2010). This was evident when we received a pair of half-drilled pearls, each weighing 28 carats, for testing. Although they appeared suspicious in the radiographs, it was only through careful tomographic scanning of these two pearls that we were able to identify them as beaded cultured pearls (saltwater), most probably from Pinctada maxima, known as South Sea cultured pearls in the trade.