You need to be careful about using ball bearings or marbles in larger glass paint bottles. I had a bottle of Alclad Black Primer and Microporefiller which comes in a large glass bottle. I added a small stainless bearing, because Alclad has a tendency to settle. I paint at a special workstation in my 3 car garage. I was shaking the Microporefiller bottle vigorously at my workbench, when the ball bearing inside sheared right through the shoulder of the bottle, and a stream of black Primer shot out across my garage, hit the ceiling, and came down across the hoods of two cars, in a perfect black line about 1/2 inch wide! It was quite a mess to clean up. It was also across my hand, sleeve and workbench. Fortunately, the bottle didn't shatter in my hand, it just had a round hole the size of a dime in the shoulder of the bottle! I notice now that Alclad includes ball bearings in its Microporefillers. Instead of shaking paint by hand, I always use my Robart paint shaker-- it does a better job of mixing than ball bearings.