arcanist

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 […]

Ringler has the merit of having raised himself from a common potter to an “Arcanist,” as the Germans term one who is the sole depositor of an important secret;

A person who studies arcana or religious mysteries.

[Catechumens] had Prayers for themselves, but were not admitted to hear the Prayers of the Faithful, which were peculiar to the Celebration of the Eucharist, from which Catechumens were excluded, But all this was, and might be done, without favouring in the least the vain Pretences of the Modern Arcanists: For in all this there was no Design to conceal such Mysteries as the Worship of Saints, and Angels, and Images, from the Knowledge of the Catechumens;

There were on this Occasion not far from us some of the Clergy, […] and also Arcanists or Dealers in Mysteries;