Aqua regia
When Germany invaded Denmark in World War II, the Hungarian chemist George de Hevesy took the Nobel Prize medals of Max von Laue and James Franck to keep them safe. De Hevesy dissolved the medals, which were made of gold, into aqua regia. He did this so the Nazis would not steal them. He placed the jar that held the solution of aqua regia and gold on a shelf in his laboratory at the Niels Bohr Institute. The jar looked the same as hundreds of other jars in the laboratory, so the Nazis thought that all the jars had normal chemicals in them. After the war, de Hevesy returned to the lab, found the jar with the solution, and removed the gold from it. He returned the gold to the Royal Swedish Academy of Sciences, and the Nobel Foundation used the gold to make new medals for Laue and Franck.