When choosing gold jewelry, it is very important to test the purity of the material. The following are some commonly used methods for testing the purity of gold jewelry materials:
First, visual inspection
Observe the color and luster:
The higher the purity of gold is, the darker its color is usually. For example, gold with a purity of over 95% presents a deep reddish yellow color. Gold with a purity of 90% to 95% has a slightly reddish to light yellow color. Gold with a purity of 80% to 85% is light yellow in color.
Check the discoloration situation:
Check whether there is obvious discoloration in the worn areas or edges on the surface of the gold. If the golden color gradually fades and turns into another color, it might be a gold-plated product.
Second, magnet test
Pure gold is non-magnetic. Bring a strong magnet close to a gold product. If the product is attracted, it is not gold. However, it should be noted that even if goldware cannot be attracted by a magnet, it does not mean it is pure gold, as it may contain other non-magnetic metals.
Third, hardness testing
Pure gold has a low hardness. Shallow marks can be made by fingernails and tooth marks can be left by biting (but this method is not recommended as it may damage the teeth. Moreover, gold processed with special techniques such as 3D hard gold has a higher hardness and is not suitable for this method). Gold jewelry with high fineness is softer than that with low fineness. The more copper it contains, the harder it is.
Fourth, density test
Weighing: Use a balance to measure the mass of the gold product.
Measure the volume: Fill a small bottle with water and record the initial water level height. Put the gold product into the measuring bottle, record the water level height again, and calculate the increase in water volume corresponding to the change in water level.
Calculate the density: Use the formula "Density of the metalwork = Total weight of the metalwork ÷ Volume increase of water" to calculate the density. The density of pure gold is approximately 19.32 grams per cubic centimeter. If the density is close to this value, it may be real gold or a metal with a density close to that of gold.
Fifth, the burning method
Pure gold is refined at extremely high temperatures and then cooled. It does not change color when exposed to fire. Heat the gold jewelry to be identified red-hot with fire, and observe the color change after it cools down. If the surface still retains the original golden color, it is pure gold. If the color darkens or turns black to varying degrees, it is not pure gold. However, it should be noted that the burning time should not be too long to prevent the gold from deforming.
Sixth, chemical reagent testing
Bromine chemical test: Put the gold jewelry into the alcohol solution, shake it slightly, and then immerse a piece of filter paper into the solution. The filter paper will turn grayish purple. Then drop 4 drops of bromine-A reagent onto the filter paper. If the test paper turns white, it can be initially determined to be gold jewelry.
Nitric acid test method: Place the gold ware in a small stainless steel container, add a drop of nitric acid, and carefully observe the reaction. If the area where acid drops appears green, the goldware may be made of ordinary metal or a gold-plated product. If the area where acid drops appears golden, it is gold-plated copper. If the area where the acid drops shows a milky color, it is gold-plated silver. If there is no reaction at the place where the acid is dropped, then the goldware may be real gold. However, it should be noted that nitric acid is somewhat dangerous and difficult to obtain. Safety must be ensured during operation.
Seventh, ceramic scratch test method
If a black scratch appears when an unglazed ceramic is scratched over a gold product, it indicates that the product is not gold. If there is a golden scratch, it proves that the product is made of gold. However, this method may cause slight scratches on the goldware, so it should be used with caution.
Eighth, identification of electronic gold testers
The electronic gold detector is a highly precise instrument for testing the purity of precious metals such as pure gold, K gold, platinum, palladium and silver. There are often distinctions between density method gold analyzers and fluorescence spectrometry gold analyzers:
Density-based gold detector: By using Archimedes' principle, it preliminarily determines the type of metal by comparing the density of an unknown metal substance with the fixed density of precious metals in nature.
Fluorescence spectrometer (XRF) : It uses an X-ray detector to detect various energy-characteristic X-rays emitted by the sample, and analyzes the energy magnitude and intensity of the output signal of the detector through an energy spectrometer to conduct quantitative and qualitative analysis of the sample.
Ninth, the touchstone comparison method
The touchstone comparison method is a traditional identification method. By grinding a gold medal of known fineness with the sample to be tested on a touchstone and comparing the depth of the color left by the grinding track, the fineness of the sample can be initially judged.
Tenth, professional institution testing
The most authoritative and accurate method is to send gold jewelry to a professional jewelry appraisal institution for testing. These institutions will adopt advanced testing equipment and technologies, such as X-ray spectrometers, to conduct non-destructive tests on samples and accurately analyze the gold content and other impurity components in the samples.
Precautions
Some testing methods may cause damage to gold jewelry, and there is a risk for non-professionals to operate. When conducting a gold purity test, it is recommended to seek professional help.
Genuine gold jewelry usually has purity marks, such as 999 pure gold, AU999, G999, etc. These marks can be used as a reference when making a purchase.
Through the above methods, you can conduct a preliminary test and judgment on the purity of the material of gold jewelry. To ensure the superior quality of the purchased gold jewelry, it is recommended to choose a reputable jeweler or brand and keep the purchase vouchers and certificates well.