(historical) A craftsman who has knowledge of a manufacturing secret (specifically in the area of porcelain manufacturing).
1799, William Tooke (translator), The Life of Catherine II. Empress of Russia, by Jean-Henri Castéra, London: Longman and Rees, 3rd edition, Volume 1, Preliminaries, Section 3, p. 36,
The porcelain manufactory likewise entertains, excepting the modellers and arcanists, none but russian workmen […]
A person who studies arcana or religious mysteries.