There is a Chinese profession that has been kept secret for centuries but is still transmitted to Vietnam and what is it?

Mulberry growing, silkworm rearing, and silk weaving first appeared in human history in China nearly 5,000 years ago. After centuries of trying to keep this profession a secret under the Chinese feudal regime through many dynasties, finally the occupations of mulberry growing, silkworm rearing, and silk weaving were spread to Korea in the 4th century, then later on. expanding to other countries, including Vietnam. Currently, there are over 60 countries with mulberry growing, silkworm raising and silk weaving, of which 10 countries have the highest output in the world. In Vietnam, the profession of growing mulberries and raising silkworms has been around for a long time and has become a traditional profession. According to the Ministry of Agriculture and Rural Development, the whole country currently has 32 provinces with mulberry growing and silkworm raising, with 38,076 farming households working in mulberry growing and silkworm raising, calculated by labor, accounting for 0.24% ...