I've been only using castor oil to my lashes at night, and my lashes are getting longer and thicker!!! yay!!!
Since castor oil is heavy, I don't dip into the bottle, I pour a little bit on the lid, then gently swipe it with the disposable masacara wand then apply it. If it looks to heavy, then I gently dab off the excess on the lashes.
I started to apply castor oil on my eyebrows too at night, and I'm starting to see a little bit of growth (which is great news because my eyebrows are too thin)