I. Introduction of spectroscope

Spectroscope is a small, portable instrument for analyzing the light passing through gemstones. It detects the principle related to "spectrum", the optical property of gemstones. It can be used to identify the gemstone type, the chromogenic element in the gemstone, whether it is dyed or optimized, and in the case of gemstone varieties of typical spectrum, it can also be used to identify its subspecies.

Raster spectroscope

Prism spectroscope

The first image above shows the most common raster spectroscope, and the table spectroscope below. Raster spectroscopes are very portable and look similar to dichroic spectroscopes, but they allow in more light and are easier to read than prism spectroscopes, and each band in the spectrum of raster spectroscopes is roughly the same width. Since raster spectroscopes are easier to carry and less expensive, fans should start out with raster spectroscopes, or buy prisms for professional development.

Two, the principle of use

The spectroscopic observation of gemstones is based on the principle of absorption spectrum of gemstones, and the white light can be decomposed into monochromatic light of different wavelengths by using dispersion elements (triangular prism or grating), and constitute a continuous visible spectrum. All kinds of pigment ions (transitional elements, some rare elements, radioactive elements) contained in gemstones have different degrees of selective absorption of visible spectrum, and are shown in different positions of absorption lines and absorption bands in application. The absorption bands and absorption lines in the spectrum of gemstones have fixed absorption positions, which can be used to identify the variety of gemstones and the causes of color.

Raster spectroscope structure

Prism spectroscope structure

Comparison of band widths of two spectroscopes

The spectrum is the "fingerprint" of the gem. When light passes through transparent or translucent gemstones, each gemstone absorbs different objects of the monochromatic light (different wavelengths) that make up white light. This difference is caused by chromophore ions and internal structures, which we can see with the naked eye. But in practice, red spinels are often mistaken for rubies. At this time, it is necessary to observe the position of the black line or black band in the absorption spectrum of the gem through the spectroscope, which can determine the variety of the gem to a certain extent. Unfortunately, not every kind of gem can present a clear visible absorption spectrum.

Three, the use of methods

Different from dichroic mirror observation requirements can only use transmission light so strict, spectroscopic observation methods are varied.

1, transmission method is suitable for translucent to transparent gems, can ensure enough light through the gems into the spectroscope.

(1) Place the gem on the blackboard with holes;

(2) Point the light source at the gem;

(3) Point the spectroscope at the gem;

(4) Interpret the position of the absorption line in the spectroscope.

Spectroscopic transmission observation method

2. Internal reflection method is suitable for transparent faceted gems with lighter color and smaller stone particles.

Observation methods are as follows: This article is from GTC

(1) The gem table is placed downward on the black background;

(2) Adjust the Angle of the light source so that the Angle between the direction of the incident light and the spectroscope is roughly 45°.

(3) Aim the spectroscope at the gem so that as much light as possible can be reflected through the inside of the gem and enter the spectroscope;

(4) Interpret the position of the absorption line in the spectroscope.

Spectroscopic reflection observation method

　　3. Surface reflection method is suitable for gems with poor transparency, especially jade. Adjust the Angle between the direction of the incident light and the spectroscope so that as much white light as possible can be reflected off the gem surface and enter the spectroscope. The operation method is the same as the transmission light method.

Spectroscopic surface reflection observation method　　

IV precautions

1. The use of white light source (continuous spectrum) can be incandescent lamp, flashlight or special optical fiber lamp. 2. The clarity of the absorption line (band) in the spectrum is affected by the size, color and transparency of the gem. 3. Try to let the light that passes through the gem into the spectroscope. 4. The slit of the spectroscope should be kept clean. If there is dust, it will produce black horizontal lines on the spectrum. 5. When observing, do not hold small gems in hand. The blood in the fingers has absorption line (592nm), which will affect the observation, but should use gem tweezers.

Of course, Xiao Bing has also introduced before, any kind of testing instrument can not be solely responsible for the gemstone identification results, the spectroscope is the same, when can not clearly judge the results, it needs to assist other means to participate in the identification.

Spectroscopes are especially useful for synthetic diamonds, for example. Most natural diamonds have a sharp absorption band at 415mm, which synthetic diamonds do not. Some synthetic rubies also exhibit absorption bands similar to natural rubies.