This is the final fill of my alchem session. I didn't include in my window selection the section of filled bottles at the very bottom. There is one full bottles and 5 more to go. I start of this fill with quicksilver and more than 5 bottles with on colour left. It is the perfect setup for a Voodoo.
I have tried a voodoo in the middle of a session without any advantage. I ended up with 2 stars in filled bottles that started off with 3 gleams. In my experience it is best to have as many different colours in one fill that you can. And to save completely filling any bottle until the very end (when possible).