Real diamonds have sharp, bright and dazzling refracted light, while inferior goods mixed with glass and timely are obviously inferior in luster. Because this is determined by the refractive index of the material itself, it is difficult to change it by processing.
To identify masonry, you can put diamonds on a plane with handwriting, such as newspapers and magazines. If you can see the words clearly through the diamond, or you can see a rough black font, then this gem is mostly fake. Real diamonds are too refractive to see black marks or even fonts.