The Brewing Kit requires 20 Sapphires, 1 Brewing Mix Potion, 500,000 Stones and Crafting level 65 to craft.

The kit gives a 10% chance for any potion made to produce an additional Potion at no extra cost or experience gained, or 20% with a Green Brewing Kit Orb. Unlocking Hard brewing perk allows the kit giving the extra XP

It doesn't work with Mixing Potions.