A lot of fake gold jewelry has been found on the market, counterfeiting the ancient gold, which has a golden appearance, its cut is also yellow after cutting, makes it really easy to be fooled.
We bought some objects to analyze the fake pure gold jewelry and analyze its technology.
1. The first step we use the alloy curve to test the jewelry, will measure the lower content of gold, other impurities are copper, zinc, nickel, etc., and the results are as follows:
The gold content is only 2.039%.
At the same time, looking closely at the spectral shape, we find that the simulated spectrum does not match the measured spectrum at the position of the Kb peak (energy: 8.907) for copper, and at the position of the La peak (9.713) and the Lb peak (11.44) for gold.
According to the principle of the XRF fundamental parameter method (FP algorithm ), the algorithm can simulate any spectral shape according to the structure and composition of the sample and match with the measured spectrum, we use the curve of the single-layer alloy to detect and found the Kb peaks of copper don’t match , then the sample must be a multilayer structure, and at least two layers contain copper, because the characteristic intensity of copper from different layers does not have the same contribution to the spectral shape, which leads to the ratio of the Ka and Kb peaks of copper is not consistent with the Ka/Kb ratio of the single-layer copper alloy. At the same time, the gold peaks are affected by the excitation from multiple layers resulting in the simulated spectra being inconsistent with the measured spectra, then this gold must be a coating.
Conclusion: The jewelry is gold-plated, not pure gold/K-gold, and the sample contains copper in at least two layers.
2. We know that it is gold-plated jewelry, but now it is not clear how many layers there are, and the thickness and composition of each layers are unknown. In the previous step we knew that copper was present in both layers, so let's assume that this jewelry is a three-layer structure, in which a copper-zinc-nickel alloy is used as the base material, and copper is plated first, followed gold plated, and use this to create an application curve for the plating, and then open the test spectrum.
It was found that the measured and simulated spectra of the La and Lb peaks of gold matched, but the measured and simulated spectra of the Kb peak of copper still did not match.
Conclusion: Gold is plated and is a surface layer. However, the overall model is still incorrect.
3. Continuing the analysis, we know that there is a common process in the electroplating industry: on brass is first plated with copper, copper plating can form a thin layer of copper on the surface of brass, providing a good substrate and corrosion protection, followed by nickel plating to further increase adhesion and provide higher corrosion resistance. Finally, gold plating is applied to achieve the effect of a false impression. This multi-layer plating process provides better plating quality and protection, while making the metal layer more stable and durable.
Let's assume that the process is used for fake pure gold jewelry, establish a structure model with brass as the base material, first copper plated, then nickel plated, and finally gold plated.
Carefully observe the contribution of the characteristic intensity of copper from different layers to the copper peak:
In this figure, the blue spectrum indicates the contribution of the characteristic intensity of copper from the base material brass to the copper peak.
In this figure, the blue spectral shape indicates the contribution of the characteristic intensity of copper from the plating to the copper peak.
At this point, the measured spectrum matches the simulated spectrum exactly, meaning that the model is correct.
Conclusion: The fake gold jewelry is actually a brass plated with copper, then nickel and finally gold.
This kind of plating process is a very routine process, which is widely used in the industrial field. Although this kind of jewelry can deceive the human eyes by pretending to be full-gold jewelry, it has nothing to hide in front of the X-ray spectrometer.
Customers who find such cheap gold jewelry should pay special attention.