Its formula is: look at the color, weigh, listen to the rhyme, fold hard, grind on the stone, compare the cards, point with acid and fix the color. The first four sentences rely on perception and feeling; The last four sentences need tools and reagents.
According to the different luster and color of gold, pure gold, k gold, real gold and fake gold can be roughly distinguished. That is, red and yellow are the best gold, and the purity is above 95%; The fineness of positive yellow is about 80%; Cyan accounts for about 70%; Yellow is light gray, and the fineness is about 50%. Therefore, there is a formula of "seven green, eight yellow, nine five red, yellow and white with gray and half gold". For jewelry that has been hidden for a long time, there is a saying that "copper turns green, silver turns black, and gold never changes color".
Gold has the characteristics of ductility and low hardness, and can be pressed into thin sheets with a thickness of 12.7 microns. When the color is high, you can scratch it with a pin or nail to leave traces. More than 97% of colored gold jewelry is folded two or three times, and wrinkles appear at the bend, also known as fish scales; Gold ornaments with a fineness of about 95% feel hard when bending, and the scales are not obvious; About 90% of gold ornaments are hard when bending, and there are no fish scales; Gold jewelry with many impurities will break after two or three bends; If it is made of gold, it will break when bent, and there are obvious sand grains on the cross section. When using this method, the width and thickness of jewelry should be considered. Thick and wide jewelry is harder, while thin and narrow jewelry is softer.