Various detection methods for gold, silver and platinum jewelry

There are a lot of precious metal ornaments on the market. It’s really fake and false, and the ingredients are too difficult to distinguish. Now let authoritative experts introduce several detection methods to distinguish between true and false.

First, non-destructive testing

Any method of non-destructive testing of gold, silver and platinum Jewelry is not omnipotent, and there are limitations. Therefore, it is necessary to have close cooperation with various methods in order to draw a correct conclusion. For example, a hollow chicken heart was examined, and Au = 996 Å was measured by surface X-ray fluorescence spectrometry, and Au = 950 Å was measured by the inner layer.

The effective measurement of gold jewelry is to combine the quartz standard-density method and X-ray fluorescence spectroscopy, take the advantages of each method, and make up the shortcomings of this method. This is the gold jewelry testing center of Guizhou for more than ten years, testing dozens A summary of the success of thousands of gold jewelry.

(A), non-destructive testing of gold jewelry quartz standard - density method

Here, when the author is the legal person and director of the Guizhou Gold Jewelry Testing Center, the drafting by the center Hu Jiayan has been approved by the Guizhou Provincial Technical Supervision Bureau from 1996-12-12, and listed as the local standard of Guizhou Province. It was implemented on January 1, 1997. Document No. DB52/T413-1996 "Non-destructive testing method for gold jewelry - density method".

The method is applicable to the determination of gold content of gold, thousand gold rings, rings, pendants, chains, etc. It is also applicable to the determination of gold products content of 99.9% and 99.0%, and is not applicable to the determination of gold content of closed, hollow, gold-coated and gold-plated jewelry.

The method is applicable to the determination of the formula K gold and K white gold jewelry, and is also applicable to the determination of other specified formula alloys, and can measure other pure metals.

The method is suitable for density determination of gemstones, jade and other minerals, rocks and synthetic materials.

The method is based on Archimedes' law, the buoyancy is equal to the mass of the liquid discharged, the ratio of the mass of the sample (ornament) to the mass of the liquid discharged from the sample (ornament) and then the density of the liquid, which is the density of the sample (ornament). The sample (ornament) is weighed in air and in a liquid, respectively, and the difference between the two is the buoyancy of the sample (ornament) in the liquid.

Quartz standards for density methods are an innovation. The quartz standard sample should be a colorless transparent single crystal. Under the polarizing microscope, the test should be airless, liquid, solid inclusion, no microcrack, no twin, chemical purity SiO2 content of 99.9% or more, quartz standard density of 2.65g /cm3. Quartz has the characteristics of physical and chemical stability.

The liquid was analyzed for pure carbon tetrachloride. The density of carbon tetrachloride is linear with temperature. The liquid density value of carbon tetrachloride was controlled by quartz standard under different conditions of liquid temperature of carbon tetrachloride.

(B), X-ray fluorescence spectroscopy

Pure gold, sterling silver, pure platinum and uniform gold, non-uniform gold, and K gold can be effectively measured. Before the test, there must be a national standard calibration, and the standard level difference should be small to maintain the accuracy of the test. There is now a device called "small fluorescence" on the market, which has low precision and is difficult to measure for K gold.

The author introduces the author and director of the Guizhou Gold Jewelry Testing Center, which was drafted by the center Jia Liyu and Li Xingsen. It has been approved by the Guizhou Provincial Technical Supervision Bureau in 1996-12-12 and listed as the local standard of Guizhou Province. January 1, 1997 Implemented daily, document number DB52/T412-1996 "Non-destructive testing method for gold jewelry X-ray fluorescence spectrometry".

This standard specifies the method for determining the content of gold and impurity elements in gold jewelry and other gold products by X-ray fluorescence spectrometer. This standard applies to non-destructive testing of uniform components of gold jewelry.

Each element produces its own secondary characteristic X-ray (fluorescent) radiation under primary X-ray excitation. In the case of a certain excitation condition, the intensity of the fluorescent radiation is proportional to the content of the cap element in the sample. By measuring the intensity of the fluorescent radiation of each element and calculating it by a computer in a certain mathematical mode, the content of each element in the jewelry can be determined. Before and after the measurement, the structure, composition and shape of the jewelry are not changed, and the detection is non-destructive testing.

(three), X probe method

Pure gold, sterling silver, pure platinum and uniform gold, non-uniform gold, K gold can be effectively measured. Because of the point test, it is necessary to measure the average of several points, the test cost is high, the error is 0.01%, and the sample size of the instrument is tested. limit.

Second, the chemical law

1. Fire test method

Generally used for gold (rock gold, gold) test.

2. Atomic absorption spectroscopy

For the finished gold test, the test sample generally needs 2g, the sampling adopts the plum-style five-point method, the new drill bit is used for sampling, the middle point is worn, and the other four points are diagonally worn in the opposite direction. Dissolve, extract and measure according to chemical analysis steps.

Third, several simple methods

1. Touchstone method

It is an ancient method with a certain precision. It consists of touchstone (carbonaceous siliceous rock) and gold pair. In the past, banks used gold to adopt the gold-to-brand method.

The gold pair card is a standard sample marked with various colors and arranged in sequence. After the sample is inscribed on the touchstone, the color is placed on the card, and the color is not detected at the bottom. The error is <5. %.

2. Touchstone ash method gold test

Mark gold streaks on the touchstone, then fill the streaks with soot, drop a few drops of 1:1HNO3, and show the boiling. If the streaks disappear, it is copper. If the streaks do not disappear, the gold streaks are compared according to the gold streak contrast method.

3, silver reagent test silver

The method steps are:

1 Rub the silver coins or other silver products on the frosted glass sheets. The general streaks are lead gray.

2 Carefully sprinkle a small amount of silver reagent on the streaks with tweezers.

3 Gently place the cover glass to cover all the silver reagent and streaks.

4 Drop the HNO3 on the edge of the cover glass with a small dropper, and let it infiltrate into the coverslip to react with the silver reagent and the silver coin streak.

5 Carefully observe the reaction results. If silver is present, the streaks will quickly turn into blood red. If no silver is present, it will still be orange-yellow. When observed with a magnifying glass, it can be seen that the blood red reactant appears as a needle-like aggregate.

4, HNO3 + NaCl mixed droplet method gold test

The prepared HNO3+NaCl mixed droplets were used on the goldstone traces of the touchstone, and the gold was determined by the contrast method. Prepare a mixture of HNO3+NaCl in a ratio of 2/3 HNO3, 1/3 NaCl (3 g of salt in 10 ml of water).

5, fire test platinum

Platinum can only be burned in the fire and cannot be burned. After annealing, the original color tone of >900 不变 is unchanged, and the original color of 700 变 becomes black, and the false black is black and melted.

6, salt test method for platinum

Platinum streaks are engraved on the touchstone, the salt is covered on the platinum streak, and then 1:1HNO3 is added, and the salt is gradually dissolved, and the water is rinsed. > or = Pt950, the streak color is unchanged, the streaks of Pt900 are slightly blurred, and the Pt700 traces are grayish black.