Thousand-year-old-eggs (pidan), also known as century eggs and millennium eggs, are a popular Chinese delicacy. The dish is made by using a mixture of clay, ash, salt, rice hulls and quicklime to preserve duck eggs, and usually takes a few months to complete.
Chinese media recently reported that 30 companies involved in the production of pindan in Nanchang, the capital of Jiangxi Province, have been closed by authorities on strong suspicion of using industrial copper sulfate to hasten the ripening of the eggs.