Have you guys seen this?
http://www.minecraftforum.net/topic...epics-and-a-mod-download-to-make-them-usable/
Apparently Cauldrons are already in 1.9Pre2 but they simply weren't assigned a block ID. Someone made a super simple mod that adds a crafting recipes and gives them a proper ID so you can build them. More so
they're fully functional without any further modding.
Apparently you fill the cauldron with water, then mix in various ingredients - each of which add effects to the potion and changes the color. At any point you can use a bottle and scoop out some of the potion - each time lowering the liquid level in the cauldron by one, three times before it runs out. At any point you can add more water but it dilutes the potion and makes it weaker. Read the thread I posted, people have been experimenting and figuring out how to make the various potions.
It's pretty interesting, kind of makes me wish they kept the system now instead of replacing it with that little potion holder thingy in the screenshot. I hope we can still optionally mix potions in the cauldron just the for the hell of it, even if it's less effective.