I am using soft-bodied acrylic paints at the present time. I have noticed they tend to separate leaving an oily layer on top. Shaking them will eventually incorporate them once again, but an even quicker way to blend them together is to drop a few tiny pebbles into the bottle before shaking. The pebbles rock and roll inside the paint container as you shake, mixing the paint together much quicker.

So far it has worked very well for me, and I haven’t had the bottle become clogged with the pebbles…at least not yet.