1. First of all, the water mirror lenses of the old glasses in the Republic of China are glass or crystal. Tap the lens gently to hear the mellow sound and see the nicks on the surface. If the lens is made of plastic and other materials, there will be obvious cuts or scars on the damaged surface.

2. Secondly, the goggles of the old glasses in the Republic of China are brown or yellowish brown, which is caused by reflection and absorption. The color should be natural and pure, without abrupt spots.

3. Finally, the old glasses goggles of the Republic of China are hand-made, so they have high requirements in materials, techniques and details. We can judge whether it is handmade by looking at the patterns on the frame, the radian of the temples and the traces in the production process.