At uni, I took a survey engineering course. The Prof, named Gerhart (spg?) Gloss had been a German Airman prisoner of war in WW2. He and his buddies made a makeshift camera and used urine to develop photos of the camp and surrounding countryside and got them smuggled back to the Luftwaffe (spg?).

I live in New Brunswick, Canada. I have had more than one occasion of thawing out a frozen padlock or car door/trunk lock "naturally".