Pi-dan (ancient eggs/100year eggs/'horse-piss' eggs) were traditionally soaked in horse urine and buried underground to cure.These days a blend of artificial chemicals (uric acid, urea etc) is used. There have been some scandals in China with companies using poisonous chemicals in order to speed up the process. Definitely eatable (millions of people can't be wrong) but rather an acquired taste.
RE: Who are Localize-it? And what to expect in the near future