Because the gemstone selectively absorbs white light, when the white light passes through the gemstone, it will absorb some wavelengths of light, which can be observed through a spectroscope. The selective absorption of gemstones is related to the types of chromogenic elements. Therefore, spectroscope is the most powerful means to identify the true and false colors of gems, such as dyeing jadeite. In addition, many gems have characteristic absorption spectra, and their gem types can be determined by observing this spectrum. Such as ruby, almandine, garnet, emerald, zircon, green jade, olivine, apatite, blue, green sapphire, golden emerald and so on. It can be identified simply and quickly by skilled use of spectrometer. There are two kinds of spectrometers used in general laboratories: prism and grating. Spectrometer needs strong light, and cold light source is the best light source.

refractive index

Refractive index is an important optical constant of transparent gemstones and the main basis for identifying gemstones. There are two main methods to measure refractive index: one is direct measurement and the other is refractometer measurement; The other is relative measurement, which cannot be immersed in liquid. Refractometer is made according to the principle of total reflection of light. At present, the commonly used refractometer is only suitable for gems with refractive index of 1.36- 1.8 1 (the highest refractive index of the refractive oil usually used in refractometers is 1.8 1). The calculation method of the refractive index (n) of gemstones is that the ratio of the propagation speed of light in air (V 1) to that in gemstones (V2) is a constant, that is, N=V 1/V2. An isotropic gem in which light propagates with constant propagation speed and equal refractive index is called single refractive index. Anisotropic gemstones have two readings in the refractometer, and the difference between the maximum and minimum refractive index values is called birefringence. Refractometer is one of the most commonly used instruments for gemologists. It is small in size and convenient to use. He can not only measure the refractive index of faceted gemstones, but also measure the refractive index of globoidal gemstones through point measurement. The refractive index of each gemstone is very fixed (the refractive index of the same gemstone is slightly different due to the subtle differences in origin and chemical composition, but this is only in a very small and predictable floating range), so as long as you know the exact refractive index of the gemstone, you can basically know what kind of gemstone it is.

Ultraviolet fluorescence

Principle: Ultraviolet fluorescent lamp is a device that uses ultraviolet light as excitation light source to observe the fluorescence effect and phosphorescence effect of gemstones. The radiation source that emits ultraviolet rays is usually a mercury vapor lamp. They can emit ultraviolet rays in a certain wavelength range, and then they are filtered by special filters to generate long-wave ultraviolet rays of 365nm and short-wave ultraviolet rays of 253.7nm. The structure is composed of an ultraviolet light source, a black box and an observation window. Usage: put the gem to be tested under the ultraviolet lamp and turn on the power switch. Select the long wave band or short wave band as needed, and observe the luminescence of the gem from the observation window.

Others. . . A little. . . You can look at the reference materials I gave you.