For lower tiers, completing mastery of one tier allows you to start working on mastery of another tier. To use your Artisan example, a jeweller who has not completed Artisan mastery cannot start working on Master mastery, but one who has begun working on Artisan mastery must have completed the mastery of Expert, Journeyman, and Apprentice tiers.
Originally Posted by ParrotGuy
For tiers 6-8 (Supreme, Westfold, Eastemnet), there are some recipes that cannot be learned until the mastery of that tier is completed. Mostly these are guild recipes for the gold crafted relics (Symbol of Battle, etc). In order to learn these recipes at all, you'll need to complete mastery in the recipe's tier and all previous tiers.
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