by ThMick
I used to have that problem with polly s and floquil acrylics. The emulsion (water) of your paints is evaporating, causing them to thicken. 1 or 2 drops of denatured alcohol in a bottle, then shaking to heck out of it, will lower the surface tension of the paint enough to stop bubbles from forming or staying formed long enough to frell up your finish, without thinning the paint too much.