Battery operated Paint shakers

I have a paint sturer from badger and I really like it. It has a long rod that sticks out of a handle. The end has a round flat piece of metal. You stick the end in the open paint bottle and turn it on. In about 5 to 10 seconds all the paint and pigment are blended together perfectly. I then wipe off the paint from the rod, stick it into my windex brush cleaner bottle and turn it on again. In seconds it is as clean as new.   Greg

Personally, I don't recommend shaking paint to mix it. One of the reasons is that it gets a lot of air into the paint, making volume measurments highly inaccurate, and making it a bear to brush. Another is that it is almost impossible to adequately mix the paint by shaking. Stirring, by any method, is much to be preferred.

I agree here.  I have a robart paint shaker that I used on some of my Vallejo paints -- a couple of them were shaken so much, that it took a couple of weeks to get the air out of them.  However, if you have decided them while the bottle is inverted, you can get a lot of air out of the hit, and get a pretty creamy mix for brushing.  If you're going to use something like this, I recommend only shaking them for approximately 2-5 seconds.  Doesn't sound like a lot, but when you are shaking a bottle at ~5000 reps a minute, it can be significant.

Another reason to stir rather than shake the paint: My experience with shaking the paint is that it causes a little bit of paint to seep between the cap liner and the lip of the bottle, no matter how tightly capped the bottle. So I'd use the paint, put the lid on, and next time I'm ready to use that color, the lid is practically welded onto the bottle and it's nearly impossible to get off, especially with my small, weak hands. Stirring the paint has greatly reduced the stuck-lid syndrome for me.