Distinguish the authenticity of gold ingots: the density of gold is 19.32g/cm3, which is about twice as heavy as that of silver, lead and tin with the same volume. Available formula: the mass (gram) of a certain gold jewelry is equal to the density compared with the volume (cubic centimeter) of a certain gold jewelry. Calculate the density of the measured gold jewelry. If the density is about 19.32g/cm3, it is pure gold or relatively pure gold, otherwise it is impure gold or colored gold (this method is not destructive to jewelry).

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".

The color of gold jewelry is determined by grinding the gold card (the gold medal whose color has been determined) and the measured jewelry on the touchstone and comparing the colors. The method should be carried out under natural light and fluorescent lamps, not under direct sunlight and incandescent lamps.