Colored gemstones can appear as similar stones of different colors, but the chemical properties of these gems give them each their unique characteristics. Therefore, identifying a colored gemstone is not just about matching the color with a name, but also about determining whether a colored gemstone is natural or man-made. Synthetic gemstones are made to resemble real gemstones, but the chemical properties of synthetic and real gemstones are inherently different. With the proper equipment and knowledge of gemstones, you can differentiate between natural and synthetic gems.
Examine the gemstone through the Chelsea filter. A Chelsea filter is a color filter only filters dark red and yellowish-green light. Real and synthetic gems react differently to the light, which can help identify a real colored gemstone versus a fake one. It can also help you tell if the color of the stone was treated in some way.
Use the loupe to spot inclusions in the gemstone and other flaws. Hold the gem steady under the loupe, and hold the loupe an inch from your eye and the gem an inch from the loupe. Inclusions help identify gemstones, and the lens on a 10x triplet-type loupe provides magnification to help spot obvious or surface flaws in the stone. The stone will likely have flaws, but for example, if the stone resembles a gemstone that is supposed to be an eight on the hardness scale and is covered with scratches, it can indicate that it is glass and not a stone.
Examine the gemstone under the ultraviolet lamp. The ultraviolet lamp will help differentiate real gemstones from fake ones by determining whether the stone has color that can't be seen in ordinary light, a term known as fluorescence.
Examine the gemstone using a dichroscope. After you concur that the gemstone is real, you need to differentiate the gem from other gemstones that share the same color. The dichroscope will help you tell the difference between green gemstones based on how they refract color from different directions and the different shades of green present in the stone, a characteristic known as pleochroic.
Measure the refractive index (R.I.) of the gemstone using a refractometer. The R.I. measurement reveals a gemstone's brilliance by comparing angle that light hits the stone compared to the angle that the light is refracted. Every gemstone has a different R.I. measurement, so once you confirm that the gem is real, the refractometer can help determine which gemstone it is. However, a refractometer cannot find the R.I. measurement of a stone like a diamond because the brilliance level is too high.
Examine the gem under the binocular microscope. The binocular microscope shines light on the top of the gem and features both bright-field and dark-field illumination, which can help you find and view inclusions of other mineral or flaws in the gemstone. Rarely are natural gemstones flawless, therefore, an absence of flaws can indicate that the gem is a fake. At the same time, not all gems features inclusion, while some gemstones almost always features a certain type of inclusion, which can help identify the stone. (See Reference 3, page 30; See Reference 2, page 18)