You need to talk to the professor in the academy once you got the quest for it (the quest is 1 of the 3 quests for the resistant armor types). After that you need to build the mine near Begus in order to fill up the buckets.
(at least thats what I remember from my play thru not 100% sure tho)
Thanks for the info but I still don't understand how to make the bucket, cuz the walktrough says the recipe is part of the quest but I don't have it I think. Cuz it doesn't show up anywhere