How are pearls identified?
Pearl Introduction
Figure 1 Various pearls
The name of pearl comes from Latin, which means “the pride of the sea”. Pearls are different from other gemstones. They are round, soft in color, shining, white and beautiful. They are beautiful and precious ornaments without any processing. Since ancient times, they have been cherished by humans. People call pearls the “queen” of gemstones. They are a dazzling pearl among gemstones, and are also the birthstone for June and the commemorative stone for the 30th anniversary of marriage.
How to identify
Only gemstones that meet all of the following data and meet the identification characteristics of pearls are pearls.
- Refractive index of pearls
The refractive index of pearls is measured using a gem refractometer (Figure 2). Since pearls are organic gems, it is generally not recommended to test the refractive index. If testing is required, the refractive oil must be cleaned immediately after the test.
The refractive index (Figure 3) was measured as 1.54 by spot method, and the birefringence was unmeasurable.
Figure 2 Gemstone refractometer |
Figure 3 Refractive index readings |
- Optical characteristics of pearls
The optical characteristics of gemstones are mainly detected through a gem polariscope (Figure 4).
The optical characteristics of pearls are: inhomogeneous aggregates. Since pearls are generally opaque, they are unmeasurable.
Figure 4 Gemstone Polariscope
- Ultraviolet fluorescence of pearls
Pearls fluoresce under ultraviolet fluorescent light, as measured by ultraviolet fluorescent light (Figure 5). Black pearls show weak to moderate red and orange-red fluorescence under long-wave ultraviolet light. Other pearls show light, yellow, green, and pink fluorescence ranging from none to strong.
Figure 5 UV fluorescent lamp
- Pearl density
The density of pearls is measured by a density balance (Figure 6). The density of pearls is between 2.60 and 2.85 g/cm3, and the density of pearls of different types and origins will vary slightly. The density of natural seawater pearls is 2.61 to 2.85 g/cm3, and the density of natural freshwater pearls is 2.66 to 2.78 g/cm3, and rarely exceeds 2.74 g/cm3.
Figure 6 Density balance
- Magnification inspection
Magnified observation is one of the most effective methods for identifying pearls. The magnified characteristics of pearls are checked by a gemological microscope (Figure 7).
Figure 7 Gemstone microscope
- When natural pearls are magnified, shingled and layered growth textures can be seen on the surface (Figure 8).
Figure 8 Surface shingled and layered growth texture
- The color of dyed pearls is obviously darker at the holes and defects (Figure 9)
Figure 9 The color of the defective area is obviously darker