Recently I've happened upon a good deal for some Vallejo paint sets - the US "regular" set, and the WWII allies set. The WWII allies set has some surprisingly vibrant greens that I plan to use for a model in the very near future, but I can tell that they need to be shaken up pretty well, and I'd like to get some agitators in each of the bottles.
I've been doing research on the recommended materials, and the most recommended is the stainless steel balls. I see that Army Painter sells sets of these, but I understand there's a chance (especially for cheaper sets of them) that the "stainless" is a lie and that you have to test them with magnets before you use them as agitators. This is an option for me, since I'm probably going to have to obtain magnets for my mini bases anyway.
Another popular option that I'm seeing a lot is hematite beads. They work well and are guaranteed not to rust, but apparently they are magnetic in and of themselves, and can pull the metallic components out of paints. I have some metallics and am planning to get more in the future, so I'd rather just buy one big set of these that I can use for all of my paints, rather than having to pick and choose.
The option I'm most interested in is glass, which is pretty affordable, won't interact with any of my acrylics, and (of course) won't rust. My only concern is that tons of shaking might break down the glass balls and disperse glass bits throughout the paint. Is this an unreasonable concern? They'd just be bouncing against the plastic, after all. If anyone has experience using glass agitators let me know your results.
I even saw a Youtube video recommending small rocks from outside as agitators - but I'm even more afraid of these breaking down than the glass balls.
If anyone has any input on this subject, it is greatly appreciated. Thank you in advance for your help.