Us crafters have to save money where we can and while some waste is inevitable, too much is not good!
I have a few small bottles of Acrylic paints, general use ones that I dip into now and again. (Will be using them more once I get my airbrush!)
Various brands and varying viscosity. Therein lies the problem. I noticed that not only are they sometimes quite thick but that sometimes the pigment separates.
Now, with acrylics, you can thin with water but that is of no use if, after shaking it like a lunatic for several minutes, the water is still on top and the paint on the bottom.
Enter the solution.
Ball bearings. They must be stainless steel though, and if, like me you get them loose from a bicycle shop (enterprising, hmmm?) it is a good idea to give them a wipe in a paper towel to clean off any grease. Add a couple to each bottle, top up with water if needed and shake to mix. Many will realise how effective this is, from using bottles of nail polish with the same system.
While you are at it, clean away any crusted paint from the bottle neck and lids. If it is stubborn, use some nail polish remover. Don't use alcohol, it makes acrylic go like chewing gum!