Step 5: encase
Traditionally century eggs were rolled in mud then wrapped in rice husks and buried for a few more weeks. In this modern version I simply wrapped the eggs in several layers of clear plastic wrap then encased in modeling clay. This inhibits oxygen from reaching the eggs while they cure.
Be careful when encasing in clay as not to break the eggs. After wrapping I put all the eggs into a resealable bag and left for another 2 weeks.