I downloaded the following from Walther's.com today: Paint Stirring Before starting any painting project, make sure your paint is thoroughly mixed in the jar. Your best bet is to shake it for a couple of minutes so the pigments and base are completely blended. Motorized paint shakers help greatly as they shake it faster. Stirring paint isn't the best method as it allows more air in the mix. One easy way to aid paint mixing is to drop a couple of BBs or stainless steel ball bearings into each jar when you open it; these help stir up the thicker pigments at the bottom of the jar as you shake it.
But I found one better last week. I was (carefully) opening a rattle can that plugged up on me to salvage any remaining paint and the rattle-ball. When I retrieved the ball, I found that it was a glass marble, not a ball-bearing. Later that day, on a trip to the local Dollar Shop, I scored a bag of marbles (100-count) for a buck. Being glass, they're also less likely to break the paint jar. And at a penny each, they're a lot cheaper than stainless ball-bearings!
Regards,