In the game when you have officially become a member of the Order of the Virtous Brotherhood and can get rewarded for vampire slaying with their dust as proof and also you have to be the Mages University guild master.
Once a week in arch travens room there is a magic chest which can multiply ingredients like vampire dust which gives you about a dozen more vampire dusts, which in total can reward you 200 gold by giving it to the new head of the Order of the Virtous Brotherhood.
Remember once you have placed your item in the chest for 24 hours not to keep your ingredients in there over a week otherwise they will be destroyed.
Like I said before remember you can only multiply these ingredients once a week exactly.