For a few years we had lots of ducks and hence, for part of the year, very many duck eggs.
Many of these eggs were fried, boiled, scrambled, and used to make wonderful fluffy double-layer sponge cakes.
I remember helping to preserve some of the remaining eggs by rubbing them all over with a waxy substance called Ke-Peg. They were then stored in a box in the pantry. I think it worked by sealing the eggshell to stop air getting in, and also to stop the egg drying out.
The Ke-Peg did seem to work, though the eggs were not exactly as fresh and lovely as the advertisement claimed.