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Why were Venetian glassworkers forbidden to leave Venice or share their methods?

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fish of core-made glass — glassware Fish of core-made glass with “combed” decoration, Egyptian, New Kingdom, 18th dynasty (c. 1363–46 bc). In the British Museum. 0.141 m × .069 m.

Venetian glassworkers were forbidden from leaving Venice or sharing their techniques to protect the city's highly valued trade secrets and maintain its monopoly on the production of fine glassware.21

During the 15th and 16th centuries, Venetian artisans perfected highly sought-after techniques, most notably the creation of cristallo—a clear, colorless glass that mimicked the appearance of rock crystal—as well as complex methods like millefiori and latticinio. Because these products were in high demand across Europe, the Venetian government sought to control the industry's profits and prestige by restricting the movement of skilled craftsmen.231

To enforce these regulations, the authorities on the island of Murano imposed severe penalties on any glassmaker who attempted to defect or teach their methods to outsiders, with punishments extending to the workers' families. Despite these strict laws, many artisans eventually fled to other regions, such as Altare, which helped spread the Italian art of glassmaking throughout Europe and led to the development of the façon de Venise style.23