Laboratory Identification - Jadeite

Jade is very popular in my country and the market demand is enduring. The National Jewelry Testing Center (NGTC) has tested a large number of jade jewelry. Today, we will introduce to you how natural jade and artificially treated jade are identified and distinguished in the laboratory.

1. Laboratory Identification Steps

According to the national standard GB/T16553 "Jewelry and Jade Identification" and the laboratory's "Jade Testing Process", important identification items for jadeite identification include magnification inspection, fluorescence observation, infrared spectroscopy, ultraviolet-visible absorption spectroscopy testing, etc. In addition, comprehensive tests will be conducted on jade's refractive index, density and other spectroscopic characteristics.

It should be emphasized that the test conclusion is drawn from a comprehensive analysis of multiple test data. In other words, the conclusions drawn from a single, one-sided detection method are unreliable.

2. Commonly used identification methods

1. Magnification inspection

The first thing to do with a sample is to observe it with the naked eye, observing its surface and internal features. Natural jade has a fiber-interwoven structure and a glassy luster. However, after being soaked and corroded by strong acids and alkalis, the internal structure of jade is destroyed, becoming loose and fragile, and needs to be filled with resin and other materials to present a resin or waxy luster. The filling will cover the cracks, but under magnification, spider-web-like acid etching marks can still be seen on the surface, microscopic cracks can be seen on the polished surface, and the internal structure is loose.

For dyed jadeite, the dye enters the jadeite along the cracks and is distributed in a silk screen pattern. Nowadays, dyeing is often carried out at the same time as bleaching and filling, and sometimes the abnormal color distribution is more obvious. When examining the coated jadeite under magnification, the color is uniform, with a resinous luster and no granularity, and bubbles or peeling of the coating may be visible.

2. Fluorescence Observation

Ultraviolet fluorescent lamp is a more traditional jadeite detection tool. Natural jade usually has no ultraviolet fluorescence, or has weak white, green or yellow fluorescence. Most jadeite that has been filled has medium or strong fluorescence, but with the improvement of counterfeiting technology, the fluorescence of recently processed jadeite has become weaker and weaker, or even has no fluorescence.

3. Infrared spectrum test

Infrared spectrometer is the most commonly used and effective large-scale equipment for jade identification. The molecules or functional groups in jewelry and jade each have their own infrared absorption region in the infrared absorption spectrum. In other words, through the infrared spectrum, we can quickly and accurately determine the species of the sample.

Infrared spectrometers are very sensitive to organic compounds, especially high molecular weight polymers. Filled jadeite contains high molecular polymer materials and has specific absorption peaks.

4. UV-visible absorption spectrum test

UV-visible absorption spectroscopy testing is the most effective means of identifying dyed jadeite. Taking green jadeite as an example, natural green jadeite has absorption lines or bands at 630nm, 660nm, and 690nm, while green jadeite dyed with chromium salts has an obvious wide band visible at 650nm. Jade dyed with other types of dyes also has ultraviolet absorption characteristics that are different from its natural counterparts.

3. Some questions about jade identification

1. Can jadeite be identified using only Raman spectroscopy?

Raman spectroscopy can be used to determine whether a sample contains artificial resins such as epoxy resin. At the same time, it can also be determined whether it has been coated. However, for jadeite, infrared spectroscopy can completely solve these tasks independently, which means that Raman spectroscopy is an auxiliary means in jadeite detection.

In addition, auxiliary tests on jadeite can be carried out using instruments such as color filters, cathode luminescence devices, and X-ray fluorescence spectrometers.

2. Can jadeite be identified only by refractive index and density?

First of all, density and refractive index are not fixed values. They fluctuate within a certain range due to factors such as mineral composition, structure, and chemical composition. After jade has been processed, the test values ​​of its density and refractive index will not necessarily exceed the normal range, which means that jade samples with normal density and refractive index are not necessarily without artificial processing.

The testing of jewelry and jade cannot be based on just one or two pieces of data to draw conclusions. During the identification process, a variety of technical means should be used to analyze various data in order to reach a correct conclusion. Jade is no exception.

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