X-ray microradiography
GIA calls microradiography the most reliable non-destructive way of seeing the internal structure of pearls, and says it can also help separate natural-color from treated-color pearls.
What the X-rays show
Nacre is denser to X-rays than organic material and voids, so it shows up lighter in the image. Cultured pearls often show telltale features: a bead nucleus, voids, or linear structures. Natural pearls more often show small, irregular growth structures. The separation is not always straightforward, and when results are unclear, micro-CT scanning gives the best data (GIA).
Detecting treatments
- Dye: a gemologist can detect dyed pearls in most cases (GIA). Dye can collect in the drill hole and in pits or cracks (Jewelry Business).
- Bleaching: routine and, for one-step bleaching, virtually impossible to detect (GIA).
- "Chocolate" pearls: GIA identified bleached Tahitian cultured pearls using UV fluorescence, spectroscopy and trace elements.
When to get a report
- Before paying a natural-pearl price.
- For golden South Sea or dark pearls where natural color matters.
- To settle an inheritance or insurance question.
