I wrote this post originally in July 2011. I'm reposting this method as it really works and I needed to give my paint brushes a little bit of extra love! I still use this method for cleaning my paint brushes when I haven't taken the best care of them.
Here’s a great method for reviving a well used, hard and/or inflexible paint brush. Generally you should wash your paint brushes in warm soapy water immediately after painting with water based paints (acrylic, alkyl, chalk, milk paint or gesso etc). If extra scrubbing is required to clean your brush, use a nylon filament fingernail brush or similar. Never use a wire brush. You can also use an old hair comb to spread the filaments during cleaning. Failure to adequately clean your brush can cause a build up of paint in the heel of the brush, causing the brush to become stiff.
After almost ten months of full time painting, my brushes were looking a bit worse for wear. I had painted my kitchen cabinets, the skirtings and mouldings of my house as well as all the furniture on my blog (till July 2011) using the three paint brushes below. So they were doing okay but really needed a good clean. I always wash my brushes after use but sometimes I'm in a rush (generally painting till the nth minute and then racing to get to school pick up) and I don't wash my brushes well enough around the ferrule. My brushes weren't totally inflexible but the paint building up around the ferrule meant that they weren't painting like a new brush would.
Time to freshen them up with hot vinegar. You can use any white vinegar - go ahead and buy the big plastic cheap bottle rather than the more expensive glass bottle - I also use white vinegar for cleaning my bathroom and my kitchen. To be honest white vinegar is white vinegar!
This method will also work if you have forgotten to wash your paint brush after painting.
Pour white distilled vinegar into a saucepan and heat over the stove. You could also heat the vinegar in the microwave.
Once the vinegar is hot (simmering or boiling), pour it into an old bowl, jar or container. Place your brush in the hot vinegar. Let sit for at least 20 minutes until the paint softens. You should really suspend your paint brushes with a bull dog clip so the bristle aren't touching the sides. This will mean the bristles don't get out of shape. I have before just rested them in an old butter container and not suspended them and the bristles were fine.
Once the brushes have finished soaking, wash them in warm soapy water (I use dishwashing liquid). Use your fingers to remove the old paint. If you use a nail brush, make sure you only brush down the hairs of the paintbrush as you don't want to "fluff" up the fibres. Do not use excessive force -you are better off to take care of the bristles and repeat the method than damaging your brush. Rinse thoroughly to remove all the paint and the soap. If you do get any stray hairs poking out just snip them off with scissors. You can also scrub the handles with steel wool to clean them up also.
Rinse thoroughly and let dry by setting the paint brush on a flat surface.