Single and double layer mug identification

1. From the inside observation: Due to the double-layer structure, the volume of the double-layer cup is smaller than that of the single-layer mug. The inner wall and the outer wall are at a certain Angle, while the inner and outer walls of the single-layer cup are parallel. And the naked eye can also roughly estimate the thickness of the cup wall, single, double wall is at a glance.

2. View from the bottom: Secondly, there is an obvious way to look at the bottom of the cup, because the double layer between the inside and outside of the cup is empty, so it needs to be communicated with the atmosphere (if sealed, it will be due to the existence of the pressure difference, and the ceramic is relatively fragile, it may crumble), so there will be a small hole at the bottom of the cup, which is also the difference between single and double layer cups tips.