No matter how well you clean your paint brushes, sometimes they simply wear out. Especially when dealing with modern acrylic paints, some things simply take their toll over time. Still, there are ways to fix them, and get far more use of those often expensive paint brushes.
Some make the mistake of leaving their brushes soaking in water too long. My children have a horrible habit of doing this to mine when they borrow them. You should never leave brushes in water for more than a few minutes, If you do (or someone you love does), this can lead to two major problems. The following article deals with the more common occurrence – damaged bristles.
If brushes are abandoned in a container of water, the bristles of the brush become bowed, separated, frayed, or misshapen in some manner. This can result from mere minutes left soaking. You should clean brushes immediately after each use.
Another thing that can damage bristles is allowing paint to dry on them. This is another thing my children seem to love to forget, so in both of these instances, I have been forced to find ways of dealing with it, and saving my precious brushes as best I can. I have found two methods of dealing with this. If the first does not work, I use the second, which is definitely the more rigorous of the two, as it involves chemicals.
Simple cleaning method
The simplest way of dealing with damaged bristles, especially if the paint has not completely covered and dried into them, is too wet the bristles, and gentle work a mild detergent or soap through them. This can take time, as you must work the soap through the bristles thoroughly, all the way to the core. You may also need to rinse the brush out completely, then repeat the process one or more times.
Heavy duty cleaning
If this still does not work, or if the paint is obviously thick and dried into the bristles, they may need to be restored through the use of solvents. For acrylic paints, and any other water based paints, my suggestion here would be denatured alcohol. This substance can be purchased at art, craft & hobby stores, and often at hardware stores and the painting department of other stores. It will often loosen these hardened paints from the bristles, and can even restore brushes to tip top shape if applied correctly.
One important thing to remember, is not to allow the ferule or handle to soak in the alcohol, only the bristles themselves. Otherwise, this may damage the rest of the brush. The easiest way I have found to achieve this is a jar or cup with a metal coil across the top that holds the brushes at the desired level while the alcohol does its work. This metal coil can be as simple as an old binding from a spiral bound notebook.
After the brushes have soaked for an hour or so, check to see if the paint has loosened. If it has not, they may need to soak overnight. Either way, when most of the harder paint has dislodged itself, you can then wash the brush again with a mild soap as before, and store it properly, which means in an upright position, so that the bristles can dry without becoming malformed in any way.
These are the best methods I have discovered to date for dealing with paint build up from years of use, and painting mishaps that can result from forgetfulness or carelessness as well. They can help renew old brushes, and rescue forgotten ones, leaving years of quality usage for brushes that may have otherwise been thrown away. However, you should always remember to be safe when dealing with solvents such as denatured alcohol.
Source : Over 30 years as an artist, crafts-person, and trainer of others in these fields as well.