I've shaken the bottles manually for years, but I finally got sick of that and decided to go for a mechanical solution.
This is a very cheap jigsaw. Brand new, it cost me about twenty-five bucks, but if you're even stingier than that, they're easy enough to come by second-hand.
I wrapped the blade with multiple layers of masking tape. This serves several functions:
- I'm less likely to accidentally cut myself (or anything else)
- It provides a visual guide as to where the blade buries itself into the body of the machine. A paint bottle can't go below that point or it will be knocked off as the blade oscillates.
- It provides a fairly good non-slip padded surface to keep everything in place while the saw is running.
I considered attaching some rubber non-slip mat with double-sided tape, but I haven't found that necessary — the masking tape appears to do the job adequately.
I experimented with various means of attaching the paint bottles — rubber bands (too fiddly), little spring clamps (OK, but too small a contact area, and they tended to crush the bottle) — and finally settled on this one. It's a simple paper clip with a long curved barrel that provides good, firm attachment. I haven't yet had a bottle come free using this.
For best results, one should add one or two agitators to each bottle of paint — short lengths of pewter sprue work well. But I've got a lot of bottles of paint, so I tend not to bother except with especially problematic mixes. This thing will give me the equivalent of half an hour of manual shaking in about 30 seconds, and it generally does the job just fine.
One note: I've found that vigorous shaking sometimes seems to pressurize a bottle of acrylic paint slightly, probably due to bubbles forming. If there's paint in the neck of the dropper, this can cause a small volcano of paint when the bottle is opened, so I've taken to whacking the bottle base-down on my workbench a couple of times after shaking just to clear the dropper before opening.