[NGTC Research News] Detection of Bottom Covered Jadeite

The coated jade is also called “dressing” jade, which is coated with a green film on the surface of natural colorless or light-colored jade products to pretend to be natural high-grade jade. Since the durability of the coated jadeite is poor, the film tends to fall off over time. Consumers and even jewelers often buy such “high-end” jadeites in the market, resulting in large economic losses.

Recently, the National Jewelry Quality Supervision and Inspection Center has identified a number of covered jade ring faces with copper support. The color is green, the structure is finer and more cotton, but the transparency is better. Different from the traditional coated jadeite, this kind of jadeite is only covered at the bottom. It is not easy to find after inlaying. It is very confusing. It is easy to observe it as a natural untreated high-grade jade. Therefore, the author summarizes the treatment characteristics of such coated jadeite, and gives some warnings to merchants, jewelry testing stations and consumers.

Identification feature

In this paper, the detection of this batch of jadeite is described in detail from three aspects: infrared spectroscopy, magnifying observation and ultraviolet fluorescence characteristics.

1, infrared spectrum

The samples were identified by infrared spectrometer reflection method, and the infrared spectrum features were all characteristic peaks of jadeite. Since the bottom of the sample was sealed and infrared spectral transmission detection was not possible, we used a diffuse reflector to detect these samples. The test results show that the transmission spectrum of this batch of samples seems to have no problem from the surface, but the absorption peaks at 2910cm-1, 2970cm-1, 3015cm-1 and the absorption of wax at 2850cm-1, 2920cm-1, 2957cm-1 exist. difference. Therefore, we suspect that other organic compounds other than wax exist.

So, we carried out further tests on the samples.

Figure 1: Infrared Spectral Reflectance Spectra of Inlaid Jadeite Samples

Figure 2: Infrared Spectral Diffuse Reflectance Spectra of Inlay Jadeite Samples

2, amplification detection

Visually, the green color of the entire ring face was slightly oily, but there was a hint of positive green from the inside. There is no coating on the table and the peeling of the film layer. However, it was also observed that the front and side colors of the ring face were inconsistent. On the side view, the color of the ring face was significantly lighter.

Under the microscope, the unremoved inlaid sample was magnified from the side, and the green film layer was faintly visible at the bottom of the sample, and the film peeled off locally.

In order to further verify whether there is a film treatment, we will disassemble the sample after consulting the customer. A magnified view under the microscope shows that the entire jadeite is covered with a green film and there are signs of film shedding.

Figure 3: Green film visible from the side of the inlaid jade sample and the film peeled off

Figure 4: The body of the inlaid jade sample is fluorescently inert, and a green fluorescence is visible between the ring and the support.

3, UV fluorescence

Under the UV fluorescent lamp, the undisassembled jade sample body is fluorescently inert, but exhibits strong green fluorescence between the jadeite and the setting. The disassembled jade sample can see strong green fluorescence at the bottom of the jade, and there is a clear boundary between the green film and the jade body. Through the mottled fluorescence, it is also possible to judge the phenomenon of film shedding.

in conclusion:

After testing in the above aspects, the jade sample was treated with a film to treat jade.

to sum up:

The jadeite that is generally covered by the film is covered with a colored film on the jade as a whole to cover up the lack of color, light color or color shift of the jade itself. The treatment of the bottom of the color film has higher requirements for processing the sample. Usually the sample to be treated is a ring face, and the texture and transparency are good, so that the green color of the colored film can be fully reflected, so that the appearance is more "high-end". The jade ring surface treated by this treatment method is very confusing and difficult to find once the bottom layer of the colored film layer is covered by the mosaic of the back cover (or even the inlay).

For this relatively concealed coated jade, if you see the jade color from the side is different from the front, you should be vigilant. In laboratory conditions, amplification inspection, infrared spectroscopy and ultraviolet fluorescent lamps are useful detection methods. However, under non-laboratory conditions, unless you have a wealth of experience, it is difficult to make accurate judgments. Consumers are advised to require merchants to provide identification certificates issued by authoritative quality inspection agencies such as NGTC to avoid or reduce losses.

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