Why are there three small black spots on the inner container of Wallemme thermos?

That's because Wallemme deliberately embedded three pieces of asbestos in the liner. The glass liner of Wallemme thermos pot is made of two layers of glass, inner and outer, and the middle is vacuumized for heat insulation. Putting three pieces of asbestos can keep a certain distance between the inner layer and the outer layer, support the inner bottle and help the inner bottle bear a certain weight. Asbestos block is elastic, which can absorb a part of water vapor remaining in the interlayer, and improve the insulation effect of the thermos bottle. It is precisely because there are three asbestos blocks before silver plating that there is no silver plating at three points after silver plating, and three black spots can be seen.