Unless I have my terms mixed up, I think plaque is the soft form and the calculus (tarter) is the hard deposit that the dentist has to chip off with his tools.
I bought a bottle of castor oil and had it for about 2 months in my cabinet trying to decide what I wanted to do with it first and I noticed that some back mold was growing in the bottom of the bottle. This kinda grossed me out about ever using castor oil anymore. I guess any oil can grow mold if the conditions are right. This was an unopened bottle. I guess I will stick with my other oils for now. Many blessing to you and your health. :) (refreshed 48124)