Preserved eggs are not intentionally added with lead and cannot be formed during processing. When processing preserved eggs, soda ash, lime, salt and yellow lead powder should be mixed in a certain proportion, and mud and bran should be wrapped outside the duck eggs. Two weeks later, the delicious preserved eggs are ready. Plumbum preparatium powder is lead oxide, which can make eggs produce beautiful patterns, but with Plumbum preparatium powder, preserved eggs will be polluted by lead. The functions of lead oxide in preserved egg processing are as follows: ① promoting and guiding the alkaline components in the feed liquid to penetrate into the egg. (2) Make preserved eggs turn quickly, with deep color and long aftertaste. (3) Keep the preserved egg protein to a certain hardness, so that the preserved egg protein does not stick to the shell and is easy to shell. ④ Make preserved eggs have the same maturity and easy to master, and ensure the stability of product quality.