Soak eggs in clear vinegar for around 1 to 3 days prior to use, making sure the eggs are completely covered. After soaking the first day, use gloves and remove any scum that has built up on the surface. Top up with vinegar or replace with fresh vinegar. Finally, gently buff the eggs with a soft sponge to remove any trace of shell. Most of it dissolves. The final egg has a clearer membrane than if hydrochloric acid is used.