Russian IDA-64 rebreather mask from the 1960s.
How do you stop your mask from misting up underwater?
Different diving organisations and instructors have various remedies such as wiping saliva round the inside of the mask and then rinsing it in sea water or using a commercial defogging preparation or using baby shampoo instead of saliva.
This Russian mask is a wonderful alternative — it has a small “windscreen wiper” on the inside of the mask. Simple technology that never caught on!