Attempt to create a ferrofluid gone wrong.

I used the process described here to create a ferrofluid. I ended up with a very viscous, brown liquid which was insoluble in kerosene. I have enough materials to try again, but I'd like to know what I did wrong. My theories:

• Boiled at too high a heat for too long, boiling off water as well as ammonia.

• Didn't boil long enough, not allowing the oleate ions to bind to the magnetite.

• Didn't sufficiently mix the oleic acid.