This factory for the production of a local delicacy called "Imperial eggs" or "Sunhuadan."
Delicacy of course on the fan, well, apparently they have it yummy. What is this delicacy, read on.
To this dish mainly use duck eggs which are soaked for 40-60 days in a liquid mixture consisting of caustic soda, salt and tea leaves, or mixture of thick wrap caustic salts and wheat husk. After 2-3 weeks, preserved eggs are obtained, the protein which becomes smoother, firmer and gets a clear dark brown, and the yolk turns into a blue-black gelatinous substance. Chinese cuisine admirers say that this is an incredibly tasty treat, especially when using it with a mixture of vinegar sauce, ground ginger and soy sauce.