Minecraft wiki entry for Before_1.9, associated text: Potions have four tiers, those being base, extended, level II, and reverted. On most potions, extended is obtained by adding a piece of redstone to the potion in the brewing stand, while level II requires a glowstone dust. If an extended potion receives a glowstone dust, or a level II potion receives a piece of redstone, it will change to the other effect if available, or become a reverted potion.