By paint I mean like house / deck paint. Not artsy fartsy paint.
If the paint is still wet and it's latex paint, plain water will remove it. (Sometimes you have to add soap.) If it's oil-based paint or if the paint is dry, paint solvent will remove it. (You can buy this at most hardware stores.) If both fail, time for a new brush.
Good question. I'm wondering the same thing myself. I have washed, soaked, re-washed and dried paintbrushes, which still have paint in them. And it's latex paint which I thought was easier to clean up...
Gently wash your brushes in warm, soapy water (using dish soap) before the paint has had a chance to dry. Rinse them with clean water. This works well for latex or water-based paints. Good luck!
Go to HD or Lowe's and pick up a can of brush cleaner. Let the brushes soak, then scrub them with steel wool. This will get just about all of the paint out. To make brushes easier to clean, keep the following in mind. Buy good brushes, such as Purdy or Wooster. They are much easier to paint with than cheap brushes and clean much easier. Dip the brush into the paint an inch or so. Getting paint up to the grommet doesn't make the painting go any easier or faster, but it does make them a bear to clean. Clean the brushes immediately when finished. If you take a break while painting, load the brush with paint and wrap tightly in a plastic bag. If stopping for the day but coming back to the same paint the next day or the day after, load it with paint, wrap it in a bag, and store it in the freezer. Take it out an hour or so before you start painting again. Hope this helps.
I assume you mean latex paint. First: when painting the bristles should not be dipped in the paint more than halfway. This will keep the paint from over accumulating on the brush and will help avoid dripping. It is important to rinse the brushes thoroughly after use. Keep rinsing until the water runs completely clear. It takes a long time but it's worth it. Once it gets to a point where the water is only slightly cloudy I usually fill a bowl with water and press the brush from side to side against the bottom until the water gets almost opaque, dump the bowl and refill repeating until all paint has lef the brush. If you use the brushes for an extended period you may want to change brushes and soak the used ones to avoid having the paint dry around the upper bristles and ferrule (the metal part). Then when the job is done, wash all the brushes at once. If the paint is already dried you can remove enough of it to make the brush usable again by combing the paint out with a painters comb or brush. You can usually buy them at any store that sells paint supplies. Soak the brush in warm water for about 10 minutes or so, then run the comb through the bristles from the ferrule to the ends until they are pliable and mostly paint free, rinsing often. You will have some speckles left on the bristles, but the brush will be usable.