Gold with purity above pure gold should not blacken after burning, but blackening does not necessarily mean it is a fake. There are many reasons for blackening after burning, such as solder joints, insufficient gold content and dirt on the surface.

To clean the gold ornaments, you can soak a piece of flannel in toothpaste until it shines, or soak it in hot solution for 2 hours. Hot solution should be prepared in advance. 1 00g water should be added with15g bleaching powder,15g sodium bicarbonate and 5g salt, and then washed with hot water and sodium bicarbonate solution (1kg water).