What do you think of the hotel mirror? Is it a double mirror?

See if there is a distance between your finger and the finger in the mirror. Normal mirror, with a certain distance. Double mirrors, fingertips seamlessly connected. Cover the mirror with your nails. If there is a distance between the mirror and the nail, it is a one-sided mirror and can be used safely. If there is no distance between the mirror and the nail, it is a double mirror.

Because ordinary mirrors have a reflective layer in front of the glass, the reflective layer is generally plated on the back, so it is separated by the thickness of a piece of glass. If a layer of glass is added in front of the double mirror, or the coating is a "sandwich" in the middle of the glass, this method will not work. The double-sided mirror uses about 50%~70% reflective layer, so it is darker than the ordinary mirror. Take out the cosmetic mirrors you carry with you and compare them together to see if there is a big difference in brightness.