The salted eggs are prepared by first mixing soil with water to obtain mud. Then salt is added to the mud and mixed together. Fresh duck eggs are individually dipped and packed in wooden boxes. Once the box is completely full it is sprayed one last time with salt.
These eggs are stored indoors at room temperature over the next 20 days. That way the salt works its way into the eggs uniformly.
They can be made of duck eggs or chicken eggs. The commercial salted eggs are mostly duck eggs and always dyed red to differentiate from fresh eggs.